Whoever accepts His testimony has certified that God is truthful.

John 6:27
Do not work for food that perishes, but for food that endures to eternal life, which the Son of Man will give you. For on Him God the Father has placed His seal of approval."

John 8:26
"I have much to say about you and much to judge. But the One who sent Me is truthful, and what I have heard from Him, I tell the world."

Romans 4:11
And he received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. So then, he is the father of all who believe but are not circumcised, in order that righteousness might be credited to them.

Romans 15:28
So after I have completed this service and have safely delivered this bounty to them, I will set off to Spain by way of you.

1 Corinthians 9:2
Even if I am not an apostle to others, surely I am to you. For you are the seal of my apostleship in the Lord.

2 Corinthians 1:22
placed His seal on us, and put His Spirit in our hearts as a pledge of what is to come.

Ephesians 1:13
And in Him, having heard and believed the word of truth--the gospel of your salvation--you were sealed with the promised Holy Spirit,

Ephesians 4:30
And do not grieve the Holy Spirit of God, in whom you were sealed for the day of redemption.

2 Timothy 2:19
Nevertheless, God's firm foundation stands, bearing this seal: "The Lord knows those who are His," and, "Everyone who calls on the name of the Lord must turn away from iniquity."

1 John 1:10
If we say we have not sinned, we make Him out to be a liar, and His word is not in us.

1 John 5:10
Whoever believes in the Son of God has this testimony within him; whoever does not believe God has made Him out to be a liar, because he has not believed in the testimony that God has given about His Son.

Revelation 7:3
"Do not harm the land or sea or trees until we have sealed the foreheads of the servants of our God."

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