"The people of Constantinople, and almost everywhere, assemble together on the Sabbath, as well as on the first day of the week, which custom is never observed at Rome or at Alexandria." —Socrates, "Ecclesiastical History," Book 7, chap.19.
The World
"For although almost all churches throughout The World celebrated the sacred mysteries (the Lord's Supper) on the Sabbath of every week, yet the Christians of Allexandria and at Rome, on account of some ancient tradition, refuse to do this." The footnote which accompanies the foregoing quotation explains the use of the word "Sabbath." It says: "That is, upon the Saturday. It should be observed, that Sunday is never called "the Sabbath' by the ancient Fathers and historians." Socrates, "Ecclestical History," Book 5, chap. 22, p. 289.
Constantinople
"The people of Constantinople, and almost everywhere, assemble together on the Sabbath, as well as on the first day of the week, which custom is never observed at Rome or at Alexandria." Sozomen, "Ecclesiastical History," Book 7, chap. 19.
The World - Augustine, Bishop Of Hippo (North Africa)
Augustine shows here that the Sabbath was observed in his day "in the greater part of the Christian world," and his testimony in this respect is all the more valuable because he himself was an earnest and consistent Sunday-keeper. See "Nicene and Post-Nicene Fathers," 1st Series, Vol.1, pp. 353, 354.
Pope Innocent (402-417)
Pope Sylvester (314-335) was the first to order the churches to fast on Saturday, and Pope Innocent (402-417) made it a binding law in the churches that obeyed him, (In order to bring the Sabbath into disfavour.) "Innocentius did ordain the Saturday or Sabbath to be always fasted." Dr. Peter Heylyn, "History of the Sabbath, Part 2, p. 44.
5th Century Christians
Down even to the fifth century the observance of the Jewish Sabbath was continued in the Christian church. "Ancient Christianity Exemplified," Lyman Coleman, ch. 26, sec. 2, p. 527.
In Jerome's day (420 A.D.) the devoutest Christians did ordinary work on Sunday. "Treatise of the Sabbath Day," by Dr. White, Lord Bishop of Ely, p. 219.
France
"Wherefore, except Vespers and Nocturns, there are no public services among them in the day except on Saturday (Sabbath) and Sunday." John Cassian, A French monk, "Institutes," Book 3, ch. 2.
Spain (400 A.D.)
"Ambrose sanctified the seventh day as the Sabbath (as he himself says). Ambrose had great influence in Spain, which was also observing the Saturday Sabbath."
Truth Triumphant, p. 68.
Sidonius (Speaking Of King Theodoric Of The Goths, A.D. 454-526)
"It is a fact that it was formerly the custom in the East to keep the Sabbath in the same manner as the Lord's day and to hold sacred assemblies: while on the other hand, the people of the West, contending for the Lord's day have neglected the celebration of the Sabbath." "Apollinaries Sidonli Epistolae," lib.1, 2; Migne, 57.
Egypt
"There are several cities and villages in Egypt where, contrary to the usage established elsewhere, the people meet together on Sabbath evenings, and, although they have dined previously, partake of the mysteries." Sozomen. "Ecclesiastical History" Book 7, ch. 19