John 21:24

This is the disciple who testifies to these things and who wrote them down. We know that his testimony is true.

John 19:35

He who saw this has testified so that you also may believe. His testimony is true, and he knows he is telling the truth.

3 John 1:12

Demetrius has a good testimony from everyone, and from the truth itself. And we also testify for him, and you know that our testimony is true.

John 15:27

You also will testify, because you have been with Me from the beginning.

1 John 1:1-2

What was from the beginning,
what we have heard,
what we have seen with our eyes,
what we have observed
and have touched with our hands,
concerning the Word of life—

1 John 5:6

Jesus Christ—He is the One who came by water and blood, not by water only, but by water and by blood. And the Spirit is the One who testifies, because the Spirit is the truth.

Treasury of Scripture Knowledge

Summary

This is the disciple which testifieth of these things, and wrote these things: and we know that his testimony is true.

Bible References

We know

John 19:35
He who saw this has testified so that you also may believe. His testimony is true, and he knows he is telling the truth.
1 John 1:1
What was from the beginning,
what we have heard,
what we have seen with our eyes,
what we have observed
and have touched with our hands,
concerning the Word of life—
1 John 5:6
Jesus Christ—He is the One who came by water and blood, not by water only, but by water and by blood. And the Spirit is the One who testifies, because the Spirit is the truth.
3 John 1:12
Demetrius has a good testimony from everyone, and from the truth itself. And we also testify for him, and you know that our testimony is true.

Holman Christian Standard Bible®, Copyright © 1999, 2000, 2002, 2003, 2009 by Holman Bible Publishers.