New Living Translation
All who believe in the Son of God know in their hearts that this testimony is true. Those who don’t believe this are actually calling God a liar because they don’t believe what God has testified about his Son.

American Standard Version
He that believeth on the Son of God hath the witness in him: he that believeth not God hath made him a liar; because he hath not believed in the witness that God hath borne concerning his Son.

Berean Study Bible
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.

Douay-Rheims Bible
He that believeth in the Son of God, hath the testimony of God in himself. He that believeth not the Son, maketh him a liar: because he believeth not in the testimony which God hath testified of his Son.

English Revised Version
He that believeth on the Son of God hath the witness in him: he that believeth not God hath made him a liar; because he hath not believed in the witness that God hath borne concerning his Son.

King James Bible
He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son.

World English Bible
He who believes in the Son of God has the testimony in himself. He who doesn't believe God has made him a liar, because he has not believed in the testimony that God has given concerning his Son.

Young's Literal Translation
He who is believing in the Son of God, hath the testimony in himself; he who is not believing God, a liar hath made Him, because he hath not believed in the testimony that God hath testified concerning His Son;

1 John 5:10 Additional Translations ...