Apophthegmata Partum as translated by St. Theophan the Recluse.
Chapter X. About reasoning.
115. Abba Poemen said: teaching one’s neighbor is characteristic of the sane and dispassionate, for what need is there for anyone to build another’s house and ruin his own.
291. The elder said: there is nothing poorer than the mind that philosophizes without God about the divine. Anyone who teaches in a church or in a cell must first fulfill what he speaks and teaches, as it is said: “The husbandman that laboureth must be first partaker of the fruits” (2 Tim. 2:6).
