Augustine of Hippo a.d. 354–430
Those holy angels come to the knowledge of God not by audible words, but by the presence to their souls of immutable truth, i.e., of the only-begotten Word of God; and they know this Word Himself, and the Father, and their Holy Spirit, and that this Trinity is indivisible, and that the three persons of it are one substance, and that there are not three Gods but one God;