If there is any division between a Muslim and a Christian on the grounds of dogma, belief, ethics or morality, then the cause of such conflict could be traced to an utterance of Paul found in his books of Corinthians, Phillipians, Galatians, Thessolanians, etc., in the Bible.
As against the teaching of the Master (Jesus) that salvation only comes through keeping of the commandments (Mathew 19:16-17), Paul nails the law and the commandments to the cross (Colossians 2:14)1 and claims that salvation can only be obtained through the death and resurrection of Jesus Christ:-
"If Christ be not risen from the dead, then our preaching is vain, and your faith is also vain."
1 Corinthians 15:14
However, many early Followers of Jesus(pbuh), such as the Carpocrates,Marcionites,Cerinthians and basolideons did not believe Jesus(pbuh) was crucified.
For more information please take a look at the following articles:
Crucifixtion Or Cruci-fiction? - by Ahmad Deedat