I say, and with God's success: Tanning is the removal of the foul odor and impure moisture from the skin, and it purifies all skins that can be tanned. It is permissible to pray on them, whether the tanner is a Muslim or a non-Muslim, and whether the tanning is real with chemicals, or nominal by drying, or sun exposure, or airing. His saying : "Any hide that has been tanned is purified," in Sahih Muslim 1: 277, and Sahih Ibn Hibban 4: 104. This hadith should not be taken in its absolute sense; it is specific to skins that can be tanned. As for human skin, it is not purified by tanning due to its nobility, and likewise, pig skin is not purified due to its inherent impurity, nor is the skin of a mouse or snake purified. As for dog skin, it is purified by tanning because its essence is not impure, but its saliva is impure. Refer to: Sharh al-Wiqayah p. 100-101, Fath al-Qadeer 1: 18, Al-Hidayah 1: 20, Al-Bada'i 1: 63, Al-Mukhtar 1: 24, Al-Kanz p. 8, and God knows best.