Hippolytus of Rome

"If ye hasten to fly out of Egypt, and repair beyond the Red Sea into the wilderness," that is, from earthly intercourse to the Jerusalem above, which is the mother of the living; "If, moreover, again you return into Egypt," that is, into earthly intercourse, "ye shall die as men." For mortal, he says, is every generation below, but immortal that which is begotten above, for it is born of water only, and of spirit, being spiritual, not carnal. But what (is born) below is carnal, that is, he says, what is written. "That which is born of the flesh is flesh, and that which is born of the spirit is spirit." This, according to them, is the spiritual generation.