It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both): I heard the Prophet (peace and blessings be upon him) say: "When a skin is tanned, it becomes pure."
(b) Likewise, Malik bin Anas and Hisham bin Sa'd narrated it from Zayd: When a skin is tanned, it becomes pure.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 67