8 Many other passages, or rather all of them, attest the truth. A man, therefore, even though he will it not, is compelled to acknowledge God the Father Almighty, and Christ Jesus the Son of God, who, being God, became man, to whom also the Father made all things subject, Himself excepted, and the Holy Spirit; and that these, therefore, are three. But if he desires to learn how it is shown still that there is one God, let him know that His power is one. As far as regards the power, therefore, God is one.
But as far as regards the economy there is a threefold manifestation, as shall be proved afterwards when we give account of the true doctrine. In these things, however, which are thus set forth by us, we are at one. For there is one God in whom we must believe, but unoriginated, impassible, immortal, doing all things as He wills, in the way He wills, and when He wills. What, then, will this Noetus, who knows nothing of the truth, dare to say to these things? And now, as Noetus has been confuted, let us turn to the exhibition of the truth itself, that we may establish the truth, against which all these mighty heresies have arisen without being able to state anything to the purpose.
Source: Against the Heresy of Noetus (New Advent)