Clement of Alexandria

For there were certainly, among the Hebrews, some things delivered unwritten. "For when ye ought to be teachers for the time," it is said, as if they had grown old in the Old Testament, "ye have again need that one teach you which be the first principles of the oracles of God; and are become such as have need of milk, and not of solid food. For every one that par-taketh of milk is unskilful in the word of righteousness; for he is a babe, being instructed with the first lessons. But solid food belongs to those who are of full age, who by reason of use have their senses exercised so as to distinguish between good and evil. Wherefore, leaving the first principles of the doctrine of Christ, let us go on to perfection."