Musannaf Ibn Abi Shayba 16:541

Abu Bakr narrated to us, he said: Ibn ‘Uyaynah narrated to us, from Zayd ibn Aslam, from ‘Abd al-Rahman ibn Wa‘lah, from Ibn ‘Abbas, he said: I heard the Prophet, peace and blessings of Allah be upon him, saying: "Whichever hide is tanned, it has become pure."