This Bible contradiction is from the Skeptic's Annotated Bible.
Matthew 26:47-49 View context
And while he yet spake, lo, Judas, one of the twelve, came, and with him a great multitude with swords and staves, from the chief priests and elders of the people.
Now he that betrayed him gave them a sign, saying, Whomsoever I shall kiss, that same is he: hold him fast.
And forthwith he came to Jesus, and said, Hail, master; and kissed him.
Mark 14:43-45 View context
And immediately, while he yet spake, cometh Judas, one of the twelve, and with him a great multitude with swords and staves, from the chief priests and the scribes and the elders.
And he that betrayed him had given them a token, saying, Whomsoever I shall kiss, that same is he; take him, and lead [him] away safely.
And as soon as he was come, he goeth straightway to him, and saith, Master, master; and kissed him.
Luke 22:47-48 View context
And while he yet spake, behold a multitude, and he that was called Judas, one of the twelve, went before them, and drew near unto Jesus to kiss him.
But Jesus said unto him, Judas, betrayest thou the Son of man with a kiss?
No, Jesus identifies himself.
John 18:3-5 View context
Judas then, having received a band [of men] and officers from the chief priests and Pharisees, cometh thither with lanterns and torches and weapons.
Jesus therefore, knowing all things that should come upon him, went forth, and said unto them, Whom seek ye?
They answered him, Jesus of Nazareth. Jesus saith unto them, I am [he]. And Judas also, which betrayed him, stood with them.