John 3:11

3:11 I tell you the solemn truth, we speak about what we know and testify about what we have seen, but you people do not accept our testimony.

John 5:32

5:32 There is another who testifies about me, and I know the testimony he testifies about me is true.

John 19:35

19:35 And the person who saw it has testified (and his testimony is true, and he knows that he is telling the truth), so that you also may believe.

John 21:24

A Final Note

21:24 This is the disciple who testifies about these things and has written these things, and we know that his testimony is true.