Musannaf Ibn Abi Shayba 16:631

Abu Bakr narrated to us, he said: 'Abdah narrated to us, from Yahya bin Sa'id, from al-Qasim bin al-Mughirah, from 'Ali bin Rabi'ah, he said: I saw 'Ali wrapping his lower garment (izar), and I saw upon him a pair of trousers (tubban).