In the Gospels we are told of how Jesus forgave sin:
When Jesus saw their faith, he said to the paralytic, "Son, your sins are forgiven." Now some teachers of the law were sitting there, thinking to themselves, 7"Why does this fellow talk like that? He's blaspheming! Who can forgive sins but God alone?" Immediately Jesus knew in his spirit that this was what they were thinking in their hearts, and he said to them, "Why are you thinking these things? 9Which is easier: to say to the paralytic, 'Your sins are forgiven,' or to say, 'Get up, take your mat and walk'? 10But that you may know that the Son of Man has authority on earth to forgive sins . . . ." He said to the paralytic, (Mark 2:5-10)
Christians often use such verses to try and prove that Jesus is God, yet the biggest irony out of all this is that such verses debunk the very core of Christianity! Think of it, Jesus is forgiving sin BEFORE he has sacrificed himself for the sins of the world! This means that people could be forgiven of their sins without any sacrifice on the cross! Christians say there must be blood for the forgiveness of sins, Jesus had to die for us, it was the only way to be saved and to get rid of the sin etc etc, well obviously this doesn't seem to be the case now does it, because we see Jesus easily forgiving people of their sins without anyone having to die or any blood being shed!
So this proves that the sacrifice of the cross wasn't needed, the blood isn't needed, and nobody has to die.
Also be sure to visit the following article which addressed the argument of how Jesus is supposedly God because he forgave sins: http://muslim-responses.com/Forgiving_sins/Forgiving_sins_
And Allah Knows Best!