Abu al-Khayr (may Allah have mercy on him) said: I saw a leather garment on Ibn Wa'lah al-Saba'i (may Allah have mercy on him), and I touched it. He said: Why do you touch it? I asked Ibn Abbas (may Allah be pleased with them both) about it and told him that we live in the Maghrib, and with us are Berbers and Magians; we bring a ram and they slaughter it, while we do not eat their slaughtered animals, and we bring a waterskin with grease in it. Ibn Abbas (may Allah be pleased with them both) said: The Prophet (peace and blessings be upon him) said: "Tanning the hide is its purification."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4191