'Testimony is True' in the Bible

Jesus answered, "Even if I testify about myself, my testimony is true, because I know where I came from and where I am going. But you people do not know where I came from or where I am going.

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.

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