John 8:17
It is also written in your law, That the testimony of two witnesses is true — Jesus appeals to the Law of witnesses: Deuteronomy 19:15 requires two witnesses for testimony to be valid. Jesus uses this legal principle to establish the validity of his own testimony. He and the Father are the two witnesses: Jesus bears witness to himself, and the Father bears witness to him (through signs, works, and voice). The Law itself, which the Pharisees invoked (8:13), actually supports Jesus's claim.