Musannaf Ibn Abi Shayba 35:485

Abu Usama narrated to us, he said: Al-Walid ibn Kathir narrated to me, from Muhammad ibn Abd al-Rahman ibn Abi Sa'sa'ah, from Yahya ibn 'Umarah and 'Abbad ibn Tamim, from Abu Sa'id al-Khudri, that he heard the Messenger of Allah (may Allah bless him and grant him peace) saying: "There is no charity (zakat) on what is less than five wasqs of dates."