John 1:7, 19-23, 35-37

The same came for witness, that he might bear witness of the light, that all might believe through him.

And this is the witness of John, when the Jews sent unto him from Jerusalem priests and Levites to ask him, Who art thou? And he confessed, and denied not; and he confessed, I am not the Christ. And they asked him, What then? Art thou Elijah? And he saith, I am not. Art thou the prophet? And he answered, No. They said therefore unto him, Who art thou? that we may give an answer to them that sent us. What sayest thou of thyself? He said, I am the voice of one crying in the wilderness, Make straight the way of the Lord, as said Isaiah the prophet.

Again on the morrow John was standing, and two of his disciples; and he looked upon Jesus as he walked, and saith, Behold, the Lamb of God! And the two disciples heard him speak, and they followed Jesus.