Quran 4:48 An-Nisa, ayah 48 of 176

إِنَّ ٱللَّهَ لَا يَغْفِرُ أَن يُشْرَكَ بِهِۦ وَيَغْفِرُ مَا دُونَ ذَٰلِكَ لِمَن يَشَآءُ ۚ وَمَن يُشْرِكْ بِٱللَّهِ فَقَدِ ٱفْتَرَىٰٓ إِثْمًا عَظِيمًا ۝٤٨

4:48 Lo! 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.