John 3:33

Any man who has received His testimony has solemnly declared that God is true.

John 6:27

Bestow your pains not on the food which perishes, but on the food that remains unto the Life of the Ages--that food which will be the Son of Man's gift to you; for on Him the Father, God, has set His seal."

Romans 3:3-4

For what if some Jews have proved unfaithful? Shall their faithlessness render God's faithfulness worthless?

Romans 4:18-21

Under utterly hopeless circumstances he hopefully believed, so that he might become the forefather of many nations, in agreement with the words "Equally numerous shall your posterity be."

2 Corinthians 1:18

As certainly as God is faithful, our language to you is not now "Yes" and now "No."

2 Corinthians 1:22

and He has also set His seal upon us, and has put His Spirit into our hearts as a pledge and foretaste of future blessing.

Ephesians 1:13

And in Him you Gentiles also, after listening to the Message of the truth, the Good News of your salvation--having believed in Him--were sealed with the promised Holy Spirit;

Titus 1:1-2

Paul, a bondservant of God and an Apostle of Jesus Christ for building up the faith of God's own people and spreading a full knowledge of the truths of religion,

Hebrews 6:17

In the same way, since it was God's desire to display more convincingly to the heirs of the promise how unchangeable His purpose was,

1 John 5:9-10

If we accept the testimony of men, God's testimony is greater: for God's testimony consists of the things which He has testified about His Son.

Revelation 7:3-8

"Injure neither land nor sea nor trees," he said, "until we have sealed the bondservants of our God upon their foreheads."

Treasury of Scripture Knowledge

Summary

He that hath received his testimony hath set to his seal that God is true.

Bible References

Hath set

Romans 3:3
For what if some Jews have proved unfaithful? Shall their faithlessness render God's faithfulness worthless?
Romans 4:18
Under utterly hopeless circumstances he hopefully believed, so that he might become the forefather of many nations, in agreement with the words "Equally numerous shall your posterity be."
2 Corinthians 1:18
As certainly as God is faithful, our language to you is not now "Yes" and now "No."
Titus 1:1
Paul, a bondservant of God and an Apostle of Jesus Christ for building up the faith of God's own people and spreading a full knowledge of the truths of religion,
Hebrews 6:17
In the same way, since it was God's desire to display more convincingly to the heirs of the promise how unchangeable His purpose was,
1 John 5:9
If we accept the testimony of men, God's testimony is greater: for God's testimony consists of the things which He has testified about His Son.