John 21:24

This is the disciple that beareth witness of these things, and wrote these things: and we know that his witness is true.

John 19:35

And he that hath seen hath borne witness, and his witness is true: and he knoweth that he saith true, that ye also may believe.

3 John 1:12

Demetrius hath the witness of all men , and of the truth itself: yea, we also bear witness: and thou knowest that our witness is true.

John 15:27

and ye also bear witness, because ye have been with me from the beginning.

1 John 1:1-2

That which was from the beginning, that which we have heard, that which we have seen with our eyes, that which we beheld, and our hands handled, concerning the Word of life

1 John 5:6

This is he that came by water and blood, even Jesus Christ; not with the water only, but with the water and with the blood.

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
And he that hath seen hath borne witness, and his witness is true: and he knoweth that he saith true, that ye also may believe.
1 John 1:1
That which was from the beginning, that which we have heard, that which we have seen with our eyes, that which we beheld, and our hands handled, concerning the Word of life
1 John 5:6
This is he that came by water and blood, even Jesus Christ; not with the water only, but with the water and with the blood.
3 John 1:12
Demetrius hath the witness of all men , and of the truth itself: yea, we also bear witness: and thou knowest that our witness is true.

American Standard Version Public Domain