Musnad Ahmad 31:818

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Muhammad ibn Abdullah ibn Abd al-Rahman ibn Abi Sa'sa'ah narrated to me that he heard Yahya ibn 'Umarah ibn Abi Hasan and 'Abbad ibn Tamim narrating that they heard Abu Sa'id al-Khudri narrating that he heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "There is no charity (zakat) on what is less than five wasqs of dates, nor on what is less than five awaq of silver, nor on what is less than five camels."