Galatians 1:20

what I write to you, I call God to witness is all true:

Romans 9:1

I call Christ, and the holy spirit to witness with my conscience, that I speak the truth without guile, when I say,

2 Corinthians 11:31

the ever-blessed God, and father of our Lord Jesus Christ, knows that I speak truth.

2 Corinthians 11:10-11

I solemnly protest, no man shall hinder me of this applause, in the regions of Achaia.

Treasury of Scripture Knowledge

Summary

Now the things which I write unto you, behold, before God, I lie not.

Bible References

Behold

Romans 9:1
I call Christ, and the holy spirit to witness with my conscience, that I speak the truth without guile, when I say,
2 Corinthians 11:10
I solemnly protest, no man shall hinder me of this applause, in the regions of Achaia.