Musannaf Ibn Abi Shayba 35:161

Abu Dawud narrated to us, from Shu'bah, from Habib ibn Abd al-Rahman, who said: I heard Abd al-Rahman ibn al-Mas'udi saying: Sahl ibn Abi Hathma came to me, and we sat down. He narrated that the Prophet, may Allah bless him and grant him peace, said: "When you estimate (the yield of dates), take (the Zakat) and leave (a portion)."