Thus, if it is argued that urine is more impure than saliva, that is a valid point. Hair, however, cannot be treated as analogous to saliva, because saliva is secreted from within the dog, whereas hair grows on its exterior. All jurists distinguish between the two. Most of them hold that the hair of a dead animal is pure, unlike its saliva.

Al-Shāfi‘ī and most jurists hold that crops growing in impure soil are pure. At most, then, a dog’s hair grows in an impure place, like crops growing in impure soil. If crops are pure, hair has an even stronger claim to purity: crops contain moisture and softness in which the effects of impurity become apparent, whereas the dryness and solidity of hair prevent such effects from appearing.

Thus, for those of Ahmad’s followers, such as Ibn ‘Aqīl and others, who hold that crops are pure, hair has an even stronger claim to purity. As for those who hold that crops are impure, the distinction between crops and hair is what has just been explained: crops are analogous to animals that feed on impurities.

This also provides an argument on the issue. The Prophet, may Allah bless him and grant him peace, forbade the milk of animals that feed on impurities. Yet if such an animal is confined until it becomes wholesome, it becomes lawful by agreement of the Muslims. Before that, the effects of impurity appear in its milk, eggs, and sweat, manifesting the impurity’s foul smell and offensive character. Once those effects disappear, it becomes pure again, for when a ruling is established on the basis of an operative cause, it ceases to apply when that cause disappears. Hair, however, shows none of the effects of impurity whatsoever, so there is no basis for declaring it impure.