Sahih Muslim Book 003, Hadith Number 0712.
Chapter : Purification of the skins of the dead animals by tanning them.
Abu al-Khair reported: I saw Ibn Wa'la al-Saba'i wear a fur. I touched it. He said: Why do you touch it? I asked Ibn 'Abbas saying: We are the inhabitants of the western regions, and there (live) with us Berbers and Magians. They bring with them rams and slaughter them, but we do not eat (the meat of the animals) slaughtered by them, and they come with skins full of fat. Upon this Ibn 'Abbas said: We asked the Messenger of Allah (may peace be upon him) about this and he said: Its tanning makes it pure.