Apology
Tertullian (again): “Thus Christ is Spirit of Spirit, and God of God, as light of light is kindled. . . . That which has come forth out of God is at once God and the Son of God, and the two are one. In this way also, as He is Spirit of Spirit and God of God, He is made a second in manner of existence—in position, not in nature; and He did not withdraw from the original source, but went forth. This ray of God, then, as it was always foretold in ancient times, descending into a certain virgin, and made flesh in her womb, is in His birth God and man united.”
Tertullian, Apology, 21. ANF, III:34–35.