My LORD’s BibleApostolic Constitutions, Book VII 23
1But let not your fasts be with the hypocrites; for they fast on the second and fifth days of the week. But do you either fast the entire five days, or on the fourth day of the week, and on the day of the Preparation, because on the fourth day the condemnation went out against the Lord, Judas then promising to betray Him for money; and you must fast on the day of the Preparation, because on that day the Lord suffered the death of the cross under Pontius Pilate. But keep the Sabbath, and the Lord's day festival; because the former is the memorial of the creation, and the latter of the resurrection. But there is one only Sabbath to be observed by you in the whole year, which is that of our Lord's burial, on which men ought to keep a fast, but not a festival. For inasmuch as the Creator was then under the earth, the sorrow for Him is more forcible than the joy for the creation; for the Creator is more honourable by nature and dignity than His own creatures.