John Cassian, The Institutes III.1: Of the services of the third, sixth, and ninth hours, which are observed in the regions of Syria

Of the services of the third, sixth, and ninth hours, which are observed in the regions of Syria.

The nocturnal system of prayers and Psalms as observed throughout Egypt has been, I think, by God’s help, explained so far as our slender ability was able; and now we must speak of the services of Tierce, Sext, and None, according to the rule of the monasteries of Palestine and Mesopotamia, as we said in the Preface, and must moderate by the customs of these the perfection and inimitable rigour of the discipline of the Egyptians.