Surah Al Imran Tafseer

وَمَن يَبْتَغِ غَيْرَ الاِسْلَمِ دِينًا فَلَن يُقْبَلَ مِنْهُ

And whoever seeks a religion other than Islam, it will never be accepted of him,

whoever seeks other than what Allah has legislated, it will not be accepted from him.

وَهُوَ فِي الاخِرَةِ مِنَ الْخَاسِرِينَ

and in the Hereafter he will be one of the losers.

As the Prophet said in an authentic Hadith,

مَنْ عَمِلَ عَمَلً لَيْسَ عَلَيْهِ أَمْرُنَا فَهُوَ رَد

Whoever commits an action that does not conform to our matter (religion) then it is rejected