This Bible contradiction is from the Skeptic's Annotated Bible.

Verses

Before the cock crow.

Matthew 26:34 View context

Jesus said unto him, Verily I say unto thee, That this night, before the cock crow, thou shalt deny me thrice.

Luke 22:34 View context

And he said, I tell thee, Peter, the cock shall not crow this day, before that thou shalt thrice deny that thou knowest me.

John 13:38 View context

Jesus answered him, Wilt thou lay down thy life for my sake? Verily, verily, I say unto thee, The cock shall not crow, till thou hast denied me thrice.

Before the cock crows twice.

Mark 14:30 View context

And Jesus saith unto him, Verily I say unto thee, That this day, [even] in this night, before the cock crow twice, thou shalt deny me thrice.