Is it permissible to eat cheese that contains an unidentifiable rennet (enzyme), with the possibility that it was extracted from a pig, and is it obligatory to verify the source of this enzyme?

A Muslim should seek out good and lawful food. If it is made from the meat of sheep, cattle, and the like, then there is no harm in consuming it, provided it was slaughtered according to Islamic rites (dhakāh) and no forbidden substances were used in its processing. However, if the ingredients are doubtful, such as pork or carrion, then it is forbidden to buy and eat them.

If these substances are derived from a lawful animal after its proper slaughter, then there is no issue with their permissibility. But if it is believed that cheeses were manufactured using a forbidden substance from pork, or from an animal not slaughtered according to Islamic rites, then it is not permissible to use them, unless they have undergone a complete transformation (istiḥālah) before being added, in which case many scholars deem them lawful. However, if they have not been processed, or if they have been processed but not transformed into another substance, then they remain in their original state, which is impurity and unlawfulness of use.

If their status or source is unknown, then it appears they are permissible due to widespread need (ʿumūm al-balwā) and the unknown origin, and because most manufactured substances have undergone processing that transforms them from their original state. However, it is better to avoid them.

If properly slaughtered meat is mixed with carrion, or if one's sister is mixed with a stranger (in marriage), or if water is mixed with urine, then none of it may be consumed. When there is doubt regarding the permissibility of a food, inquiring about its source is legitimate. However, there is no obligation to conduct an overly meticulous search for food ingredients; it is sufficient for a person to rely on what is written on the product and to avoid anything doubtful.