Galatians 1:20

(As to what I am now writing to you, I call God to witness that I am speaking the truth).

Romans 9:1

I am speaking the truth as one in union with Christ; it is no lie; and my conscience, enlightened by the Holy Spirit,

2 Corinthians 11:31

The God and Father of the Lord Jesus--he who is for ever blessed--knows that I am speaking the truth.

2 Corinthians 11:10-11

As surely as I know anything of the Truth of Christ, this boast, as far as I am concerned, shall not be stopped in any part of Greece.

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 am speaking the truth as one in union with Christ; it is no lie; and my conscience, enlightened by the Holy Spirit,
2 Corinthians 11:10
As surely as I know anything of the Truth of Christ, this boast, as far as I am concerned, shall not be stopped in any part of Greece.