Ruling 219. The urine and faeces of an animal that habitually eats human excrement are impure. For the urine and faeces of such an animal to be considered pure, the animal must be put through a process of istibrāʾ, meaning that it must be prevented from eating impurity for some time and be fed pure food so that after that period, it is no longer considered an excrement-eating animal. The recommended precaution is to prevent an excrement-eating camel from eating excrement for forty days, a cow twenty days, a sheep ten days, a duck seven or five days, and a domestic hen three days, even if before these periods are over the animal in question ceases to be considered an excrement-eating animal.