Contradiction with John 3:11
John the Baptist affirms direct knowledge and testimony of what he has seen, contradicting his statement about not knowing in John 1:26.
John 3:11: Verily, verily, I say unto thee, We speak that we do know, and testify that we have seen; and ye receive not our witness.
Contradiction with Matthew 3:11
John the Baptist clarifies that he baptizes with water, but one mightier is coming, which he also indicates in John 1:26, yet here it sounds more definitive.
Matthew 3:11: I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and [with] fire:
Contradiction with John 1:33
John explicitly states God told him who to look for, as opposed to the suggestion of not knowing in John 1:26.
John 1:33: And I knew him not: but he that sent me to baptize with water, the same said unto me, Upon whom thou shalt see the Spirit descending, and remaining on him, the same is he which baptizeth with the Holy Ghost.
Contradiction with Luke 3:16
John the Baptist further differentiates his baptism from that of Jesus, implying more understanding than suggested in John 1:26.
Luke 3:16: John answered, saying unto [them] all, I indeed baptize you with water; but one mightier than I cometh, the latchet of whose shoes I am not worthy to unloose: he shall baptize you with the Holy Ghost and with fire:
Contradiction with Acts 1:5
It states John's baptism as distinct in purpose and understanding, contrasting the sense of uncertainty or lack of recognition in John 1:26.
Acts 1:5: For John truly baptized with water; but ye shall be baptized with the Holy Ghost not many days hence.