Tractates on the Gospel of John
TRACTATE 5 109 the truthful; and he was truthful for the very reason that he had been sent by the truth. If the truth had sent John, Christ had sent him.
(3) But what Christ does with the Father, the Father does; and what the Father does with Christ, Christ does. Neither does the Father do anything apart, without the Son; nor the Son apart, without the Father: inseparable love, inseparable unity, inseparable majesty, inseparable power, according to these words which he himself asserted, "I and the Father are one."^ (4) Who then sent John? If we should say the Father, we speak truly; if we should say the Son, we speak truly. But it is quite clear that we should say the Father and the Son. But him whom the Father and the Son have sent, that one God has sent, because the Son said, "I and the Father are one." How then did he not know him by whom he was sent? For he said, "I knew him not, but he who sent me to baptize with water said to me." I question John. What did he who sent you to baptize with water say to you? "He upon whom you will see the Spirit descending as a dove, and remaining upon him, he it is who baptizes with the Holy Spirit." Did he who sent you, O John, say this to you? It is clear that [he said] this. Then who sent you? The Father, perhaps. God the Father is true, and God the Son is truth; if the Father sent you without the Son, God sent you without the truth. But if you are truthful precisely because you speak the truth and you speak in conformity with the truth, the Father did not send you without the Son, but the Son and the Father together sent you. Therefore, if the Son, too, together with the Father, sent you, how did you not know him by whom you were sent? He himself, whom you had seen in truth, sent you that he might be recognized in the flesh, and he said, "He upon whom you will see the Spirit descending as a dove, and remaining upon him, he it is who baptizes with the Holy Spirit."
2. Did John hear this that he might know him whom he did
5. Jn 10.30. Very literally in both Greek and Latin it is translated, "I and the Father, we are one thing."