Here is a list of quotes showing that the earliest Christians worshipped their Lord on the first day of the week.
Sabbatarians generally hold that the early Christian church faithfully observed the Sabbath day until perhaps the time of Constantine or much later. They believe that at such time, the Christian church absorbed pagan practices, of which “Sun[day] worship” was one. These historical quotes should put such ideas to rest. The dates that these were written precede the quotations.
90AD DIDACHE: “Christian Assembly on the Lord’s Day: 1. But every Lord’s day do ye gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. 2. But let no one that is at variance with his fellow come together with you, until they be reconciled, that your sacrifice may not be profaned. 3. For this is that which was spoken by the Lord: In every place and time offer to me a pure sacrifice; for I am a great King, saith the Lord, and my name is wonderful among the nations.” (Didache: The Teaching of the Twelve Apostles, Chapter XIV)
100 AD BARNABAS “We keep the eighth day [Sunday] with joyfulness, the day also on which Jesus rose again from the dead” (The Epistle of Barnabas, 15:6-8).
100 AD BARNABAS: Moreover God says to the Jews, ‘Your new moons and Sabbaths I cannot endure.’ You see how he says, ‘The present Sabbaths are not acceptable to me, but the Sabbath which I have made in which, when I have rested [heaven: Heb 4] from all things, I will make the beginning of the eighth day which is the beginning of another world.’ Wherefore we Christians keep the eighth day for joy, on which also Jesus arose from the dead and when he appeared ascended into heaven. (15:8f, The Epistle of Barnabas, Ante-Nicene Fathers , vol. 1, pg. 147)
110 AD, IGNATIUS OF ANTIOCH: “Those [Jews] who were brought up in the ancient order of things have come to the possession of a new hope, no longer observing the Sabbath, but living in the observance of the Lord’s day, on which also our life has sprung up again by him and by his death.” (Letter to the Magnesians 8). Ignatius was a direct successor of John the apostle, and a martyr for his faith. He wrote these words about 15 years after the Revelation was written.
150AD EPISTLE OF THE APOSTLES.- I [Christ] have come into being on the eighth day which is the day of the Lord. (18)
150AD JUSTIN: “He then speaks of those Gentiles, namely us, who in every place offer sacrifices to Him, i.e., the bread of the Eucharist, and also the cup of the Eucharist, affirming both that we glorify His name, and that you profane [it]. The command of circumcision, again, bidding [them] always circumcise the children on the eighth day, was a type of the true circumcision, by which we are circumcised from deceit and iniquity through Him who rose from the dead on the first day after the Sabbath, [namely through] our Lord Jesus Christ. For the first day after the Sabbath, remaining the first of all the days, is called, however, the eighth, according to the number of all the days of the cycle, and [yet] remains the first.”. (Justin, Dialogue 41:4)
150AD JUSTIN: …those who have persecuted and do persecute Christ, if they do not repent, shall not inherit anything on the holy mountain. But the Gentiles, who have believed on Him, and have repented of the sins which they have committed, they shall receive the inheritance along with the patriarchs and the prophets, and the just men who are descended from Jacob, even although they neither keep the Sabbath, nor are circumcised, nor observe the feasts. Assuredly they shall receive the holy inheritance of God. (Dialogue With Trypho the Jew, 150-165 AD, Ante-Nicene Fathers , vol. 1, page 207)
150AD JUSTIN: But if we do not admit this, we shall be liable to fall into foolish opinion, as if it were not the same God who existed in the times of Enoch and all the rest, who neither were circumcised after the flesh, nor observed Sabbaths, nor any other rites, seeing that Moses enjoined such observances… For if there was no need of circumcision before Abraham, or of the observance of Sabbaths, of feasts and sacrifices, before Moses; no more need is there of them now, after that, according to the will of God, Jesus Christ the Son of God has been born without sin, of a virgin sprung from the stock of Abraham. (Dialogue With Trypho the Jew, 150-165 AD, Ante-Nicene Fathers , vol. 1, page 206)
150AD JUSTIN: “And on the day called Sunday, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succours the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word takes care of all who are in need. But Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having wrought a change in the darkness and matter, made the world; and Jesus Christ our Saviour on the same day rose from the dead. For He was crucified on the day before that of Saturn (Saturday); and on the day after that of Saturn, which is the day of the Sun, having appeared to His apostles and disciples, He taught them these things, which we have submitted to you also for your consideration.” (First apology of Justin, Weekly Worship of the Christians, Ch 68)
150AD JUSTIN: Moreover, all those righteous men already mentioned [after mentioning Adam. Abel, Enoch, Lot, Noah, Melchizedek, and Abraham], though they kept no Sabbaths, were pleasing to God; and after them Abraham with all his descendants until Moses… And you [fleshly Jews] were commanded to keep Sabbaths, that you might retain the memorial of God. For His word makes this announcement, saying, “That you may know that I am God who redeemed you.” (Dialogue With Trypho the Jew, 150-165 AD, Ante-Nicene Fathers , vol. 1, page 204)
150AD JUSTIN: There is no other thing for which you blame us, my friends, is there than this? That we do not live according to the Law, nor, are we circumcised in the flesh as your forefathers, nor do we observe the Sabbath as you do. (Dialogue with Trypho 10:1. In verse 3 the Jew Trypho acknowledges that Christians ‘do not keep the Sabbath.’)
150AD JUSTIN: We are always together with one another. And for all the things with which we are supplied we bless the Maker of all through his Son Jesus Christ and through his Holy Spirit. And on the day called Sunday there is a gathering together in the same place of all who live in a city or a rural district. (There follows an account of a Christian worship service, which is quoted in VII.2.) We all make our assembly in common on the day of the Sun, since it is the first day, on which God changed the darkness and matter and made the world, and Jesus Christ our Savior arose from the dead on the same day. For they crucified him on the day before Saturn’s day, and on the day after (which is the day of the Sun the appeared to his apostles and taught his disciples these things. (Apology, 1, 67:1-3, 7; First Apology, 145 AD, Ante-Nicene Fathers , Vol. 1, pg. 186)
155 AD Justin Martyr “[W]e too would observe the fleshly circumcision, and the Sabbaths, and in short all the feasts, if we did not know for what reason they were enjoined [on] you–namely, on account of your transgressions and the hardness of your heart. . . . [H]ow is it, Trypho, that we would not observe those rites which do not harm us–I speak of fleshly circumcision and Sabbaths and feasts? . . . God enjoined you [Jews] to keep the Sabbath, and impose on you other precepts for a sign, as I have already said, on account of your unrighteousness and that of your fathers” (Dialogue with Trypho the Jew 18, 21).
180AD ACTS OF PETER.- Paul had often contended with the Jewish teachers and had confuted them, saying ‘it is Christ on whom your fathers laid hands. He abolished their Sabbath and fasts and festivals and circumcision.’ (1: I)-2
180AD GOSPEL OF PETER: Early in the morning when the Sabbath dawned, a multitude from Jerusalem and the surrounding country came to see the scaled sepulchre. In the night in which the Lord’s day dawned, while the soldiers in pairs for each watch were keeping guard, a great voice came from heaven. [There follows an account of the resurrection. Early in the morning of the Lord’s day Mary Magdalene, a disciple of the Lord …. came to the sepulchre. (9:34f.; 12:50f.)
190AD CLEMENT OF ALEXANDRIA: (in commenting on each of the Ten Commandments and their Christian meaning:) The seventh day is proclaimed a day of rest, preparing by abstention from evil for the Primal day, our true rest. (Ibid. VII. xvi. 138.1)
190AD CLEMENT OF ALEXANDRIA: He does the commandment according to the Gospel and keeps the Lord’s day, whenever he puts away an evil mind . . . glorifying the Lord’s resurrection in himself. (Ibid. Vii.xii.76.4)
190AD CLEMENT OF ALEXANDRIA: Plato prophetically speaks of the Lord’s day in the tenth book of the Republic, in these words: ‘And when seven days have passed to each of them in the meadow, on the eighth they must go on.” (Miscellanies V.xiv.106.2)
200AD BARDESANES: Wherever we are, we are all called after the one name of Christ Christians. On one day, the first of the week, we assemble ourselves together (On Fate)
200AD TERTULLIAN: “We solemnize the day after Saturday in contradistinction to those who call this day their Sabbath” (Tertullian’s Apology, Ch 16)
200AD TERTULLIAN: It follows, accordingly, that, in so far as the abolition of carnal circumcision and of the old law is demonstrated as having been consummated at its specific times, so also the observance of the Sabbath is demonstrated to have been temporary. (An Answer to the Jews 4:1, Ante-Nicene Fathers Vol. 3, page 155)
200AD TERTULLIAN: Let him who contends that the Sabbath is still to be observed a balm of salvation, and circumcision on the eighth day because of threat of death, teach us that in earliest times righteous men kept Sabbath or practiced circumcision, and so were made friends of God. .. …Therefore, since God originated Adam uncircumcised, and inobservant of the Sabbath, consequently his offspring also, Abel, offering Him sacrifices, uncircumcised and inobservant of the Sabbath, was by Him commended… Noah also, uncircumcised – yes, and inobservant of the Sabbath – God freed from the deluge. For Enoch, too, most righteous man, uncircumcised and inobservant of the Sabbath, He translated from this world… Melchizedek also, “the priest of most high God,” uncircumcised and inobservant of the Sabbath, was chosen to the priesthood of God. (An Answer to the Jews 2:10; 4:1, Ante-Nicene Fathers Vol. 3, page 153)
200AD TERTULLIAN: Others . . . suppose that the sun is the god of the Christians, because it is well-known that we regard Sunday as a day of joy. (To the Nations 1: 133)
200AD TERTULLIAN: To us Sabbaths are foreign. (On Idolatry, 14:6)4
220AD ORIGEN “On Sunday none of the actions of the world should be done. If then, you abstain from all the works of this world and keep yourselves free for spiritual things, go to church, listen to the readings and divine homilies, meditate on heavenly things. (Homil. 23 in Numeros 4, PG 12:749)
220 AD Origen “Hence it is not possible that the [day of] rest after the Sabbath should have come into existence from the seventh [day] of our God. On the contrary, it is our Savior who, after the pattern of his own rest, caused us to be made in the likeness of his death, and hence also of his resurrection” (Commentary on John 2:28).
225 AD The Didascalia “The apostles further appointed: On the first day of the week let there be service, and the reading of the Holy Scriptures, and the oblation, because on the first day of the week our Lord rose from the place of the dead, and on the first day of the week he arose upon the world, and on the first day of the week he ascended up to heaven, and on the first day of the week he will appear at last with the angels of heaven” (Didascalia 2).
250AD CYPRIAN: The eight day, that is, the first day after the Sabbath, and the Lord’s Day.” (Epistle 58, Sec 4)
300AD EUSEBIUS: “They did not, therefore, regard circumcision, nor observe the Sabbath neither do we; … because such things as these do not belong to Christians” (Ecc. Hist., Book 1, Ch. 4)
300AD EUSEBIUS: [The Ebionites] were accustomed to observe the Sabbath and other Jewish customs but on the Lord’s days to celebrate the same practices as we in remembrance of the resurrection of the Savior. (Church History Ill.xxvii.5)
300 AD Eusebius of Caesarea “They [the pre- Mosaic saints of the Old Testament] did not care about circumcision of the body, neither do we [Christians]. They did not care about observing Sabbaths, nor do we. They did not avoid certain kinds of food, neither did they regard the other distinctions which Moses first delivered to their posterity to be observed as symbols; nor do Christians of the present day do such things” (Church History 1:4:8).
300 AD Eusebius of Caesarea “The day of his [Christ’s] light . . . was the day of his resurrection from the dead, which they say, as being the one and only truly holy day and the Lord’s day, is better than any number of days as we ordinarily understand them, and better than the days set apart by the Mosaic Law for feasts, new moons, and Sabbaths, which the Apostle [Paul] teaches are the shadow of days and not days in reality” (Proof of the Gospel 4:16:186).
345 AD Athanasius “The Sabbath was the end of the first creation, the Lord’s day was the beginning of the second, in which he renewed and restored the old in the same way as he prescribed that they should formerly observe the Sabbath as a memorial of the end of the first things, so we honor the Lord’s day as being the memorial of the new creation” (On Sabbath and Circumcision 3).
350 AD APOSTOLIC CONSTITUTIONS “Which Days of the Week We are to Fast, and Which Not, and for What Reasons: But let not your fasts be with the hypocrites; for they fast on the second and fifth days of the week. But do you either fast the entire five days, or on the fourth day of the week, and on the day of the Preparation, because on the fourth day the condemnation went out against the Lord, Judas then promising to betray Him for money; and you must fast on the day of the Preparation, because on that day the Lord suffered the death of the cross under Pontius Pilate. But keep the Sabbath, and the Lord’s day festival; because the former is the memorial of the creation, and the latter of the resurrection. But there is one only Sabbath to be observed by you in the whole year, which is that of our Lord’s burial, on which men ought to keep a fast, but not a festival. For inasmuch as the Creator was then under the earth, the sorrow for Him is more forcible than the joy for the creation; for the Creator is more honourable by nature and dignity than His own creatures.” (Constitutions of the Holy Apostles, book 7)
350 AD APOSTOLIC CONSTITUTIONS “How We Ought to Assemble Together, and to Celebrate the Festival Day of Our Saviour’s Resurrection. On the day of the resurrection of the Lord, that is, the Lord’s day, assemble yourselves together, without fail, giving thanks to God, and praising Him for those mercies God has bestowed upon you through Christ, and has delivered you from ignorance, error, and bondage, that your sacrifice may be unspotted, and acceptable to God, who has said concerning His universal Church: “In every place shall incense and a pure sacrifice be offered unto me; for I am a great King, saith the Lord Almighty, and my name is wonderful among the heathen.” (Constitutions of the Holy Apostles, book 7)
350 AD Cyril of Jerusalem “Fall not away either into the sect of the Samaritans or into Judaism, for Jesus Christ has henceforth ransomed you. Stand aloof from all observance of Sabbaths and from calling any indifferent meats common or unclean” (Catechetical Lectures 4:37).
360 AD Council of Laodicea “Christians should not Judaize and should not be idle on the Sabbath, but should work on that day; they should, however, particularly reverence the Lord’s day and, if possible, not work on it, because they were Christians” (canon 29).
387 AD John Chrysostom “You have put on Christ, you have become a member of the Lord and been enrolled in the heavenly city, and you still grovel in the Law [of Moses]? How is it possible for you to obtain the kingdom? Listen to Paul’s words, that the observance of the Law overthrows the gospel, and learn, if you will, how this comes to pass, and tremble, and shun this pitfall. Why do you keep the Sabbath and fast with the Jews?” (Homilies on Galatians 2:17).
387 AD John Chrysostom “The rite of circumcision was venerable in the Jews’ account, forasmuch as the Law itself gave way thereto, and the Sabbath was less esteemed than circumcision. For that circumcision might be performed, the Sabbath was broken; but that the Sabbath might be kept, circumcision was never broken; and mark, I pray, the dispensation of God. This is found to be even more solemn that the Sabbath, as not being omitted at certain times. When then it is done away, much more is the Sabbath” (Homilies on Philippians 10).
412 AD Augustine “Well, now, I should like to be told what there is in these Ten Commandments, except the observance of the Sabbath, which ought not to be kept by a Christian . . . Which of these commandments would anyone say that the Christian ought not to keep? It is possible to contend that it is not the Law which was written on those two tables that the apostle [Paul] describes as ‘the letter that kills’ [2 Cor. 3:6], but the law of circumcision and the other sacred rites which are now abolished” (The Spirit and the Letter 24).
These quotes are copied from http://www.bible.ca/H-sunday.htm but the list has been shortened and some corrections made.