This is the testimony John gave when the Jews sent priests and Levites from Jerusalem to ask him, “Who are you?”
In context
17For the law was given through Moses; grace and truth came to be through Jesus Christ. 18No one has ever seen God. The only Son, who is God and rests close to the Father’s heart — he has made him known. 19This is the testimony John gave when the Jews sent priests and Levites from Jerusalem to ask him, “Who are you?” 20He confessed and did not deny it; he confessed, “I am not the Christ.” 21They asked him, “Then what? Are you Elijah?” He said, “I am not.” “Are you the prophet?” He answered, “No.”