Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter IV. How throughout the whole of Egypt and the Thebaid the number of Psalms is fixed at twelve.

Chapter IV.

How throughout the whole of Egypt and the Thebaid the number of Psalms is fixed at twelve.

So, as we said, throughout the whole of Egypt and the Thebaid the number of Psalms is fixed at twelve both at Vespers and in the office of Nocturns, 681 in such a way that at the close two lessons follow, one from the Old and the other from the New Testament. 682 And this arrangement, fixed ever so long ago, has continued unbroken to the present day throughout so many ages, in all the monasteries of those districts, because it is said that it was no appointment of man’s invention, but was brought down from heaven to the fathers by the ministry of an angel.

Footnotes

The rule of Cæsarius also prescribes twelve Psalms on every Sabbath, Lord’s day, and festival (c. 25); so also, according to the Benedictine rule, there are twelve Psalms at mattins, besides the fixed ones, iii. and xcv. (see c. 9 and 10), as there are still in the Roman Breviary on ordinary week-days.

The custom of having two lessons only appears to have been peculiar to Egypt. Most of the early Western rules give three, e.g., those of Cæsarius and Benedict, while in the Eastern daily offices there are no lections from Holy Scripture.