John Cassian, The Institutes II.18: How they do not kneel from the evening of Saturday till the evening of Sunday

This, too, we ought to know,—that from the evening of Saturday which precedes the Sunday, up to the following evening, among the Egyptians they never kneel, nor from Easter to Whitsuntide; nor do they at these times observe a rule of fasting, the reason for which shall be explained in its proper place in the Conferences of the Elders, if the Lord permits. At present we only propose to run through the causes very briefly, lest our book exceed its due limits and prove tiresome or burdensome to the reader.