In John 5:31, Jesus says self-testimony alone is invalid — the Pharisees here misapply his own words to accuse him.

John 12:17 shows the crowd bearing witness to Lazarus' resurrection — providing the external testimony that answers the Pharisees' objection.

Hebrews 12:3 calls to consider Christ who endured hostility — the Pharisees' accusation in John 8:13 is a specific instance of that hostility.