Musnad Ahmad 25:279

Yazid narrated to us, Mas'ar ibn Kidam informed us, from 'Amr ibn Murrah, from Salim ibn Abi al-Ja'd, from his brother, from Ibn 'Abbas, from the Prophet, peace and blessings of Allah be upon him, regarding the skins of a dead animal, he said: "Indeed, its tanning has removed its impurity, or its filth, or its uncleanliness."