1 John 5:10

8 the Spirit, the water, and the blood—and these three are in agreement.

9 Even if we accept human testimony, the testimony of God is greater. For this is the testimony that God has given about His Son.

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.

11 And this is that testimony: God has given us eternal life, and this life is in His Son.

12 Whoever has the Son has life; whoever does not have the Son of God does not have life.

Do read the surrounding verses too, because the context often says more than a single verse.

Compare

BSB
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.
KJV
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.
WEB
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.
ASV
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.
DARBY
He that believes on the Son of God has the witness in himself; he that does not believe God has made him a liar, because he has not believed in the witness which God has witnessed concerning his Son.
BLB
The one believing in the Son of God has the testimony in himself; the one not believing God has made Him a liar, because he has not believed in the testimony that God has testified concerning His Son.
ÅB
Den som tror på Guds Sønn, har vitnesbyrdet i seg selv; den som ikke tror Gud, har gjort ham til en løgner; for han har ikke trodd på det vitnesbyrd som Gud har vitnet om sin Sønn.
OTB
Den som tror på Guds Sønn har vitnesbyrdet i seg; den som ikke tror Gud har gjort Ham til en løgner, fordi han ikke har trodd på vitnesbyrdet som Gud har gitt om Sin Sønn.
B1930
Den som tror på Guds Sønn, har vidnesbyrdet i sig selv; den som ikke tror Gud, har gjort ham til en løgner; for han har ikke trodd på det vidnesbyrd som Gud har vidnet om sin Sønn.

Study notes (Tyndale)

Original text and word study

Cross references