11 But perhaps they will say: Well, as it is a dove, and the dove is one, baptism there cannot be apart from the one dove. Therefore if the dove is with you, or if you be yourself a dove, do you give me, when I come to you, that which I have not. You know that this is what they say; but you will presently see that it is not of the voice of the dove, but of the clamor of the raven. For attend a little, beloved, and fear their devices; nay, beware of them, and listen to the words of gainsayers only to reject them, not to swallow them and take them into your bowels.
Do therein what the Lord did when they offered Him the bitter draught, “He tasted, and spat it out;” so also you hear and cast away. What indeed say they? Let us see. Lo, says he, “You are the dove.” O Catholic Church, it is to you it is said, “My dove is one, the only one of her mother,” to you certainly is it said. Stop, do not question me; prove first whether to me it was said; if it was said to me, I would hear it at once. “To you,” says he, “it was said.” I answer, in the voice of the Catholic Church, “To me.”
And this answer, brethren, sounding forth from my mouth alone, has sounded, as I believe, also from your hearts, and we all affirmed together, yea, to the Catholic Church was it said, “One is my dove, the only one of her mother.” Apart from this dove, says he further, there is no baptism: I was baptized apart from this dove, consequently have not baptism; if I have not baptism, why do you not give it me when I come to you?
Source: Tractates on the Gospel of John (New Advent)