Dismissing then the Arians, let us see if we are forced to confess, that by the words, That they may know Thee to be the only true God, He means us to understand that the Father only is the true God, in such sense as that only the Three together, Father, Son, and Holy Ghost, are to be called God? Does our Lord’s testimony authorize us to say that the Father is the only true God, the Son the only true God, and the Holy Ghost the only true God, and at the same time, that the Father, Son, and Holy Ghost together, i. e. the Trinity, are not three Gods, but onea true God?
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: vi. de Tr. c. 9