But though we,
or an angel from heaven,
preach any other gospel unto you than that which we have preached unto you,
let him be accursed.
Galatians 1:8
By Islam denying that Christ died on the cross-it is just another attempt by Lucifer to undo the plan of salvation--via Islam.
And [for] their saying, "Indeed, we have killed the Messiah, Jesus, the son of Mary, the messenger of Allah ." And they did not kill him, nor did they crucify him; but [another] was made to resemble him to them. And indeed, those who differ over it are in doubt about it. They have no knowledge of it except the following of assumption. And they did not kill him, for certain.
Surah 4:157