But how could it come to pass, that Him of whom he said, Behold him who taketh away the sins of the world, he should still not believe to be the Son of God? For either it is presumption to attribute to Christ a divine action ignorantly, or it is unbelief to have doubted concerning the Son of God. But some suppose of John himself that he was indeed so great a prophet as to acknowledge Christ, but still as not a doubting, but pious, prophet disbelieved that He would die, whom he believed was about to come. Not therefore in his faith but in his piety, he doubted; as Peter also, when he said, Be it far from thee, Lord; this shall not be unto thee. (Mat 16:22.)
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).