Also here a more lowkey fecespost
The Didache
"But every Lord’s day . . . gather yourselves together and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. 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" (Didache 14 [A.D. 70]).
The Letter of Barnabas
"We keep the eighth day [Sunday] with joyfulness, the day also on which Jesus rose again from the dead" (Letter of Barnabas 15:6–8 [A.D. 74]).
Ignatius of Antioch
"[T]hose who were brought up in the ancient order of things [i.e. Jews] 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 [A.D. 110]).
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 to keep the Sabbath, and imposed 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 [A.D. 155]).
"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 Savior on the same day rose from the dead" (First Apology 67 [A.D. 155]).
Tertullian
"[L]et him who contends that the Sabbath is still to be observed as a balm of salvation, and circumcision on the eighth day . . . teach us that, for the time past, righteous men kept the Sabbath or practiced circumcision, and were thus rendered ‘friends of God.’ For if circumcision purges a man, since God made Adam uncircumcised, why did he not circumcise him, even after his sinning, if circumcision purges? . . . Therefore, since God originated Adam uncircumcised and unobservant of the Sabbath, consequently his offspring also, Abel, offering him sacrifices, uncircumcised and unobservant of the Sabbath, was by him [God] commended [Gen. 4:1–7, Heb. 11:4]. . . . Noah also, uncircumcised—yes, and unobservant of the Sabbath—God freed from the deluge. For Enoch too, most righteous man, uncircumcised and unobservant of the Sabbath, he translated from this world, who did not first taste death in order that, being a candidate for eternal life, he might show us that we also may, without the burden of the law of Moses, please God" (An Answer to the Jews 2 [A.D. 203]).
Eusebius of Caesarea
"They [the early 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 [A.D. 312]).
"[T]he 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 [A.D. 319]).
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 [A.D. 345]).