The Material Sufficiency of Scripture
What else is there that knoweth the deep things of God, save only the Holy Ghost, who spoke the Divine Scriptures? But not even the Holy Ghost Himself has spoken the Scriptures concerning the generation of the Son from the Father. Why then dost thou busy thyself about things which are not written? There are many questions in the Divine Scriptures; what is written we comprehend not, why do we busy ourselves about what is not written? It it sufficient for us to know that God hath begotten One Only Son.
NPNF2, Vol. VII, Catechetical Lectures, Lecture XI.12