Contradiction with Matthew 26:70
In Matthew 26:70, Peter denies knowing Jesus before one maid, whereas, in Luke 22:60, he denies the third time before a different person.
Matthew 26:70: And when he was gone out into the porch, another [maid] saw him, and said unto them that were there, This [fellow] was also with Jesus of Nazareth.
Contradiction with Mark 14:71
Mark 14:71 describes Peter cursing and swearing during his denial, which is not mentioned in Luke 22:60.
Mark 14:71: But he began to curse and to swear, [saying], I know not this man of whom ye speak.
Contradiction with John 18:27
In John 18:27, Peter denies Jesus a third time after questioning by one of the high priest's servants, differing from Luke 22:60 where it is a servant of the high priest’s relative.
John 18:27: Peter then denied again: and immediately the cock crew.