Contradiction with Matthew 26:56
This verse describes the disciples forsaking Jesus and fleeing, which contradicts John 21:20 where a disciple is seen following Jesus.
Matthew 26:56: And they that had laid hold on Jesus led [him] away to Caiaphas the high priest, where the scribes and the elders were assembled.
Contradiction with Mark 14:50
This verse states that all disciples forsook Jesus and fled, contradicting John 21:20's depiction of a disciple following Jesus.
Mark 14:50: And they all forsook him, and fled.
Contradiction with Matthew 26:35
Here, Peter insists he will never abandon Jesus, contrasting with John 21:20's portrayal of Peter being concerned with someone else following Jesus.
Matthew 26:35: Peter said unto him, Though I should die with thee, yet will I not deny thee. Likewise also said all the disciples.
Contradiction with Luke 22:33-34
Peter declares his readiness to follow Jesus to prison and death, which contrasts with his later actions and concerns as depicted in John 21:20.
Luke 22:33-34: And he said unto him, Lord, I am ready to go with thee, both into prison, and to death.