Sunday not Sabbath

The Sabbath Abolished
Here are some examples of what early Church leaders said concerning the first day of the week and Sabbath. As you can see, they emphatically rejected the Sabbath due to Biblical reasons. There is no evidence that early Christians ever observed the Sabbath or "changed" The Saturday Sabbath to Sunday. The Sabbath was simply abolished by Christ at the Cross.

100AD EPISTLE OF BARNABAS "We keep the eighth day [Sunday] with joyfulness, the day also on which Jesus rose again from the dead" (The Epistle of Barnabas, 100 AD 15:6-8).
100AD EPISTLE OF BARNABAS: Moreover God says to the Jews, 'Your new moons and Sabbaths 1 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, 100 AD, Ante-Nicene Fathers , vol. 1, pg. 147)
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)
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)
220AD 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 Didaskalia "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)
250 AD IGNATIUS: "If, therefore, those 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-whom some deny, by which mystery we have obtained faith, and therefore endure, that we may be found the disciples of Jesus Christ, our only Master-how shall we be able to live apart from Him, whose disciples the prophets themselves in the Spirit did wait for Him as their Teacher? And therefore He whom they rightly waited for, being come, raised them from the dead. If, then, those who were conversant with the ancient Scriptures came to newness of hope, expecting the coming of Christ, as the Lord teaches us when He says, "If ye had believed Moses, ye would have believed Me, for he wrote of Me; " and again, "Your father Abraham rejoiced to see My day, and he saw it, and was glad; for before Abraham was, I am; " how shall we be able to live without Him? The prophets were His servants, and foresaw Him by the Spirit, and waited for Him as their Teacher, and expected Him as their Lord and Saviour, saying, "He will come and save us." Let us therefore no longer keep the Sabbath after the Jewish manner, and rejoice in days of idleness; for "he that does not work, let him not eat." For say the [holy] oracles, "In the sweat of thy face shalt thou eat thy bread." But let every one of you keep the Sabbath after a spiritual manner, rejoicing in meditation on the law, not in relaxation of the body, admiring the workmanship of God, and not eating things prepared the day before, nor using lukewarm drinks, and walking within a prescribed space, nor finding delight in dancing and plaudits which have no sense in them. And after the observance of the Sabbath, let every friend of Christ keep the Lord's Day as a festival, the resurrection-day, the queen and chief of all the days [of the week]. Looking forward to this, the prophet declared, "To the end, for the eighth day," on which our life both sprang up again, and the victory over death was obtained in Christ, whom the children of perdition, the enemies of the Saviour, deny, "whose god is their belly, who mind earthly things," who are "lovers of pleasure, and not lovers of God, having a form of godliness, but denying the power thereof." These make merchandise of Christ, corrupting His word, and giving up Jesus to sale: they are corrupters of women, and covetous of other men's possessions, swallowing up wealth insatiably; from whom may ye be delivered by the mercy of God through our Lord Jesus Christ! (Epistle of Ignatius to the Magnesians, Chapter IX)
250AD IGNATIUS: "On the day of the preparation, then, at the third hour, He received the sentence from Pilate, the Father permitting that to happen; at the sixth hour He was crucified; at the ninth hour He gave up the ghost; and before sunset He was buried. During the Sabbath He continued under the earth in the tomb in which Joseph of Arimathaea had laid Him. At the dawning of the Lord's day He arose from the dead, according to what was spoken by Himself, "As Jonah was three days and three nights in the whale's belly, so shall the Son of man also be three days and three nights in the heart of the earth." The day of the preparation, then, comprises the passion; the Sabbath embraces the burial; the Lord's Day contains the resurrection." (The Epistle of Ignatius to the Trallians, chapter 9)
250AD IGNATIUS: If any one fasts on the Lord's Day or on the Sabbath, except on the paschal Sabbath only, he is a murderer of Christ. (The Epistle of Ignatius to the Philippians, chapter 8)
250AD IGNATIUS: "This [custom], of not bending the knee upon Sunday, is a symbol of the resurrection, through which we have been set free, by the grace of Christ, from sins, and from death, which has been put to death under Him. Now this custom took its rise from apostolic times, as the blessed Irenaeus, the martyr and bishop of Lyons, declares in his treatise On Easter, in which he makes mention of Pentecost also; upon which [feast] we do not bend the knee, because it is of equal significance with the Lord's day, for the reason already alleged concerning it." (Ignatius, Fragments)
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)
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 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).