Contradiction with Matthew 10:33
This verse says that whoever denies Jesus before men, Jesus will also deny before God in heaven, which contradicts Peter's denial of Jesus in Matthew 26:70.
Matthew 10:33: But whosoever shall deny me before men, him will I also deny before my Father which is in heaven.
Contradiction with John 18:17
This verse indicates Peter's denial similarly to Matthew 26:70, but it highlights the contradiction of Peter's earlier claim of unfailing loyalty to Jesus.
John 18:17: Then saith the damsel that kept the door unto Peter, Art not thou also [one] of this man's disciples? He saith, I am not.
Contradiction with Mark 14:31
Here, Peter insists vehemently that he will not deny Jesus, which directly contradicts his actions in Matthew 26:70.
Mark 14:31: But he spake the more vehemently, If I should die with thee, I will not deny thee in any wise. Likewise also said they all.
Contradiction with Matthew 16:16
Peter acknowledges Jesus as the Christ, the Son of the living God, showing a previous moment of strong faith that contradicts his later denial.
Matthew 16:16: And Simon Peter answered and said, Thou art the Christ, the Son of the living God.