Musannaf Ibn Abi Shayba 7:48

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Ibn Abi Layla, from ‘Amr ibn Murrah, from ‘Abdullah ibn Salamah, from ‘Ali, who said: The expiation for an oath is the feeding of ten needy persons, for every needy person half a sa’ of wheat or a sa’ of dates, regarding the expiation for an oath.