Historical records concur that the “early church” kept the Sabbath (Saturday), and that even well past the fourth century some kept both the Sabbath and Sunday side by side. A Critical History of the Sabbath and the Sunday in the Christian Church by A. H. Lewis, D.O. (The American Sabbath Tract Society, Alfred Center, New York, 1886) presents a very good picture of what occurred regarding the Sabbath and how it was replaced by Sunday when Constantine converted to “Christianity.”
The more modern Catholic Encyclopedia states on page 336 that “The obligation of rest from work on Sunday remained somewhat indefinite for several centuries.” The New Catholic Encyclopedia adds that “There is nothing to indicate that the practice of coming together on Sunday … was regarded as obligatory … during the first three centuries of the Christian Era” (p. 800).
Sunday observance came to be added to Sabbath observance in the professing Christian world (and later superseded it) due to the belief that Christ was resurrected on Sunday.
Hastings Encyclopedia of Religion and Ethics states: “Although Jewish Christianity disappeared from the West before the end of the 2nd century, there is plenty of evidence that some of its traditions persisted in the Eastern Church for two hundred years more. The Apostolic Constitutions (vii 23,26) recognized a parallel observance of the Sabbath and Sunday. [During the second, third and fourth centuries, many documents appeared purporting to be written by the apostles. Among these were the bogus ‘Apostolic Constitutions.’ They were circulated to create the impression that man-made tradition had apostolic blessing. Although deliberate frauds, these documents nonetheless express some of the religious teachings during the centuries after the death of the apostles.] And the Council of Laodicea [about 365 A.D.], while condemning a Judaizing observance of the Sabbath, marked it as a festival and a day of worship” (vol. 12, pp. 104-105).
The twenty-ninth canon of the Council of Laodicea reads as follows: ” Christians must not judaize by resting on the Sabbath, but must work on that day, rather, honoring the Lord’s day, and, if they can, resting then as Christians. But if any shall be found to be judaizers, let them be anathema from Christ” (Nicene and Post-Nicene Fathers, vol. XIV, p. 148).
So the Sabbath was still observed on Saturday centuries after the original apostles died.