The first is that they are impure in all cases, as held by al-Shāfiʿī and in one report from Ahmad, on the grounds that they are parts of a carcass.

The second is that they are pure in all cases, as held by Abū Hanīfa and in one position within Ahmad’s school, on the grounds that moisture is what causes impurity, and moisture is found only in parts through which blood flows. This is why creatures that have no flowing blood are ruled pure. Parts that contain no moisture are therefore comparable to creatures that have no flowing blood.

The third is that parts possessing sensation, such as bones, are impure, by analogy with dried flesh; whereas parts possessing only growth, such as hair, are not impure, by analogy with plants.

[Purification from Ritual Impurity by Ablution and the Ritual Bath]

Another foundational principle concerns purification from ritual impurity by ablution and the ritual bath. In this area, the hadith jurists follow practices of the Sunnah not found among others. It is enough to cite wiping over leather socks and over other garments and intervening coverings. Imam Ahmad compiled The Book of Wiping over Leather Socks, in which he cited so many texts from the Prophet (peace and blessings be upon him) and his Companions concerning wiping over leather socks, ordinary socks, and turbans—and even over women’s head coverings, as Umm Salama, the wife of the Prophet (peace and blessings be upon him), and other women used to do, and over caps, as Abū Mūsā and Anas used to do—that any scholar who reflects on them will recognize the superiority of the hadith scholars’ knowledge over that of others. Moreover, analogy plainly supports this. Those jurists who refrained from adopting these rulings did so only because they followed the reports that had reached them and, out of scrupulous caution, were too hesitant to apply analogy.

Ahmad’s position did not vary concerning what was reported from the Prophet (peace and blessings be upon him), such as the hadiths concerning wiping over turbans and socks and the prescribed time limit for wiping; his position varied only