Is it permissible to kill monkeys to extract stones from their stomachs, which are used in medicine manufacturing and sold at high prices?

There is a difference of opinion regarding the ruling on eating, selling, and the impurity of monkeys. The majority of scholars hold the view that it is forbidden to eat or sell them, and that they are impure. The Hanafis are of the opinion that carnivorous animals, such as monkeys, are impure.

Based on these issues, it is not permissible to seek medical treatment with something extracted from a monkey's body except out of necessity and in the absence of a permissible alternative, provided that its medical benefit is proven through a reliable method.

As for killing a monkey, it is permissible if it is harmful, because it is legislated to kill anything that harms human beings. If it is not harmful, then it should not be interfered with.