Unforgivable Sin
Indeed, Allah does not forgive those who associate partners with Him, but He forgives anything else for whomever He wills. Whoever sets up partners with Allah has committed a grave sin.
4:48Lo! Allah forgiveth not that a partner should be ascribed unto Him. He forgiveth (all) save that to whom He will. Whoso ascribeth partners to Allah, he hath indeed invented a tremendous sin.
4:116Lo! Allah pardoneth not that partners should be ascribed unto Him. He pardoneth all save that to whom He will. Whoso ascribeth partners unto Allah hath wandered far astray.