Musnad Abu Ya'la al-Mawsili 42:228

Zuhayr narrated to us, Waki' narrated to us, from Isma'il bin Umayyah, from Muhammad bin Yahya bin Habban, from Yahya bin 'Umarah, from Abu Sa'id, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no Zakat on what is less than five wasqs of dates or grain."