1 John 5:10

10The [one]ὁbelievingπιστεύωνinεἰςtheτὸνSonυἱὸντοῦof Godθεοῦhasἔχειtheτὴνtestimonyμαρτυρίανinἐνhimselfαὑτῷ·The [one]ὁnotμὴbelievingπιστεύωντῷGodθεῷa liarψεύστηνhas madeπεποίηκενHimαὐτόν,becauseὅτιnotοὐhe has believedπεπίστευκενinεἰςtheτὴνtestimonyμαρτυρίανthatἣνhas testifiedμεμαρτύρηκενὁGodθεὸςconcerningπερὶtheτοῦSonυἱοῦHimαὐτοῦ.

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.