Sayyiduna Ali (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) "made obligatory, upon every young and old, free and slave among those whom they provide for, a sa' of barley, dates or raisins on behalf of each person."
It is mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7683