2 Corinthians 1:19
“For the Son of God,” says he, “Who was preached among you by us, even by me, and Silvanus, and Timothy, was not yea and nay.”
For on this account he brings before them the company of the teachers also, as thence too giving credibility to the testimony by those who taught, and not who heard it only. And yet they were disciples; however in his modesty he counts them as in the rank of teachers. But what is, “was not yea and nay?” I have never, he says, unsaid what before I said in the Preaching. My discourse to you was not now this, now that. For this is not of faith, but of an erring mind.
“But in Him was the yea.” That is, just as I said, the word abides unshaken and steadfast.
Source: Homilies on Second Corinthians (New Advent)