11 And that the whole range of the doctrine of the apostles proclaimed one and the same God, who removed Abraham, who made to him the promise of inheritance, who in due season gave to him the covenant of circumcision, who called his descendants out of Egypt, preserved outwardly by circumcision— for he gave it as a sign, that they might not be like the Egyptians— that He was the Maker of all things, that He was the Father of our Lord Jesus Christ, that He was the God of glory—they who wish may learn from the very words and acts of the apostles, and may contemplate the fact that this God is one, above whom is no other.
But even if there were another god above Him, we should say, upon [instituting] a comparison of the quantity [of the work done by each], that the latter is superior to the former. For by deeds the better man appears, as I have already remarked; and, inasmuch as these men have no works of their father to adduce, the latter is shown to be God alone. But if any one, “doting about questions,” do imagine that what the apostles have declared about God should be allegorized, let him consider my previous statements, in which I set forth one God as the Founder and Maker of all things, and destroyed and laid bare their allegations; and he shall find them agreeable to the doctrine of the apostles, and so to maintain what they used to teach, and were persuaded of, that there is one God, the Maker of all things.
And when he shall have divested his mind of such error, and of that blasphemy against God which it implies, he will of himself find reason to acknowledge that both the Mosaic law and the grace of the new covenant, as both fitted for the times [at which they were given], were bestowed by one and the same God for the benefit of the human race.
Source: Adversus haereses (New Advent)