Iyād, as recorded by Muslim. And Allah Most High says:

“Those who associate others with Allah will say, ‘If Allah had willed, neither we nor our forefathers would have associated others with Him, nor would we have forbidden anything.’”

Thus they combined associating partners with Allah with declaring things forbidden. Associating partners with Allah includes every act of worship that Allah has not authorized, for the polytheists claim that their worship is either obligatory or recommended. Some worshipped others besides Allah to draw nearer to Allah through them, while others invented a religion through which they worshipped Allah, as the Christians did when they introduced new acts of worship.

Misguidance among the people of the earth originated in these two things alone: adopting a religion that Allah had not prescribed, or prohibiting what He had not prohibited.

For this reason, the foundational principle upon which Ahmad and others built their legal schools was that actions comprise “acts of worship and customary practices.” The governing rule for acts of worship is that nothing may be prescribed except what Allah has prescribed; the governing rule for customary practices is that nothing may be prohibited except what Allah has prohibited. These newly introduced observances were prohibited only because of the religious practices introduced into them as means of drawing nearer to Allah.