Musnad Ahmad 1153:1139

'Abd al-Rahman narrated to us, Malik narrated to us, from Yazid ibn 'Abd Allah ibn Qusayt, from Muhammad ibn 'Abd al-Rahman ibn Thawban, from his mother, from 'Aishah: "That the Messenger of Allah (peace and blessings of Allah be upon him) granted a concession to make use of the skins of dead animals if they are tanned."