The Sabbath and the Lord's Supper: The Ecclesiastical History of Socrates Scholasticus (c. 400 A.D.)

For although almost all churches throughout the world celebrate the sacred mysteries on the sabbath of every week, yet the Christians of Alexandria and at Rome, on account of some ancient tradition, have ceased to do this.

The ecclesiastical history of Socrates Scholasticus, bk. 5, ch. 22

(Schaff, Philip, & Wace, Henry (Eds.), A Select Library of Nicene and Post-Nicene Fathers of the Christian Church, Second Series, Edinburgh: T & T Clark, New York: The Christian Literature Company, 1890, vol. 2, p. 132).