What is the rule by which one may know what is permissible and what is forbidden among animals for eating or for buying and selling?

It is not permissible to sell animals that are inherently impure (najis al-ʿayn), such as dogs and pigs, nor that which has no recognized lawful benefit, such as insects that offer no benefit, or predatory animals and birds that are not beneficial.

As for what has benefit, its sale is permissible, such as a cheetah for hunting, an elephant for warfare, a monkey for guarding, bees for honey, and a peacock for enjoying its beauty. The sale of a monkey for play and amusement is disliked, but its sale is permissible for one who benefits from it.