Now this is the declaration of our Faith, that we say that God is One, neither dividing His Son from Him, as do the heathen, nor denying, with the Jews, that He was begotten of the Father before all worlds, and afterwards born of the Virgin; nor yet, like Sabellius, confounding the Father with the Word, and so maintaining that Father and Son are one and the same Person; nor again, as doth Photinus, holding that the Son first came into existence in the Virgin’s womb: nor believing, with Arius, in a number of diverse Powers, and so, like the benighted heathen, making out more than one God. For it is written: "Hear, O Israel: the Lord thy God is one God."
Ambrose, Exposition of the Faith 1.1.1
