Now, if some assign definite hours for prayer— as, for example, the third, and sixth, and ninth— yet the Gnostic prays throughout his whole life, endeavoring by prayer to have fellowship with God. And, briefly, having reached to this, he leaves behind him all that is of no service, as having now received the perfection of the man that acts by love. But the distribution of the hours into a threefold division, honored with as many prayers, those are acquainted with, who know the blessed triad of the holy abodes.
Clement of Alexandria
The Stromata, Book VII
Chapter VII