Abu Dawud
Zakat
Book Number: 003 / Hadith Number: 1602
Narated By 'Aisha, Ummul Mu'minin : Describing the conquest of Khaybar 'Aisha said: The Prophet (pbuh) used to send Abdullah ibn Rawahah to the Jews of Khaybar, and he would make an estimate of the palm trees when the fruit was in good condition before any of it was eaten.