Is eating a forbidden product—such as khamr (wine) and pork—still forbidden after it has been processed and its nature changed to become another, non-forbidden substance, such as "vinegar" or "salt"? Is the final product permissible? And is it permissible to use a manufactured product—such as cheese—if a forbidden substance was used in its production?

Scholars differed regarding the ruling on impure substances if they transform into other pure materials. The Shafi'is and Hanbalis maintained their impurity, except for wine that turns into vinegar on its own, which then becomes pure. As for the Hanafis, Malikis, Zahiris, Ibn Taymiyyah, and Ibn al-Qayyim, they held that such substances become pure through istiḥālah (transformation), because the ruling of impurity is linked to the original reality that has ceased with the complete transformation. Accordingly, everything that has transformed from impurities into a completely different reality becomes permissible, unless the impure substance remains in its original state, in which case its use is not permissible, unless the impure substance changes before its addition or after mixing.