witness
Compare (John 8:14). In (John 5:31).
Our Lord, defending His Messianic claims before Jews who denied those claims, accepts the biblical rule of evidence, which required "two witnesses"; (John 8:17); (Numbers 35:30); (Deuteronomy 17:6). A paraphrase of verse (John 5:31) would be: "If I bear witness of myself ye will say my witness is not true."
Compare (John 8:14).