Musannaf Ibn Abi Shayba 3:1707

'Abbad ibn al-'Awwam narrated to us, from Hilal ibn Khabbab, who said: I entered upon 'Abd al-Rahman ibn al-Aswad in al-Mada'in, and he was praying in his house upon a sheepskin pelt, with the wool side facing outward, adjacent to his feet.