How then was it that “God [θεός] was manifested in the flesh”? “By birth birth,” of course you will say. But what sort of birth do you speak of of? Surely it is clear that you speak of that from the virginity, and that that “that which was conceived in her was of the Holy Ghost...”
Gregory of Nyssa (Γρηγόριος Νύσσης). “Controversial Discourse against Eunomius” (Πρὸς Εὐνόμιον Ἀντιρρητικὸς Λογός). Patrologiæ Cursus Completus: Series Græca Prior. Ed. Migne, Jacques Paul. Vol. 45. Petit-Montrouge: Imprimerie Catholique, 1863. (Book IV, 628)
Greek text according to the Bavarian Codex, published by Jacob Gretser, 1618.