John 9:10-11
“They said unto him, How were your eyes opened? He answered and said, A man that is called Jesus.”
What do you say? Does “a man” work such deeds? As yet he knew nothing great concerning Him.
“A man that is called Jesus made clay, and anointed my eyes.”
2. Observe how truthful he is. He says not whence He made it, for he speaks not of what he does not know; he saw not that He spat on the ground, but that He spread it on he knew from sense and touch.
“And said unto me, Go, wash in the pool of Siloam.”
This too his hearing witnessed to him. But how did he recognize His voice? From His conversation with the disciples. And saying all this, and having received the witness by the works, the manner (of the cure) he cannot tell. Now if faith is needed in matters which are felt and handled, much more in the case of things invisible.
Source: Homilies on the Gospel of John (New Advent)