Augustine of Hippo
Catena Aurea · Matthäusevangelium 21
And when he was come into the temple, the Chief Priests and the elders of the people came unto him as he was teaching, and said, By what authority doest thou these things? and who gave thee this authority? And Jesus answered and said unto them, I also will ask you one thing, which if ye tell me, I in like wise will tell you by what authority I do these things. The baptism of John, whence was it? from heaven, or of men? And they reasoned with themselves, saying, If we shall say, From heaven; he will say unto us, Why did ye not then believe him? But if we shall say, Of men; we fear the people; for all hold John as a prophet. And they answered Jesus, and said, We cannot tell. And he said unto them, Neither tell I you by what authority I do these things.
(in Joan. Tr. v. 4.) John received his authority to baptize from Him, whom he afterwards baptized; and that baptism which was committed to him is here called the baptism of John. He alone received such a gift; no righteous man before or after him was entrusted with a baptism to be called from himself. For John came to baptize in the water of repentance, to prepare the way for the Lord, not to give inward cleansing, which mere man cannot do.