John 21:24
This is the disciple who testifies about these things and has written these things, and we know that his testimony is true.
John 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.
3 John 1:12
Demetrius has been testified to by all, even by the truth itself. We also testify to him, and you know that our testimony is true.
John 15:27
and you also will testify, because you have been with me from the beginning.
1 John 1:1-2
This is what we proclaim to you: what was from the beginning, what we have heard, what we have seen with our eyes, what we have looked at and our hands have touched (concerning the word of life --
1 John 5:6
Jesus Christ is the one who came by water and blood -- not by the water only, but by the water and the blood. And the Spirit is the one who testifies, because the Spirit is the truth.