Abu Dawud
Commercial Transactions
Book Number: 016 / Hadith Number: 3406
Narated By 'Aisha, Ummul Mu'minin : The Prophet (pbuh) used to send Abdullah ibn Rawahah (to Khaybar), and he would assess the amount of dates when they began to ripen before they were eaten (by the Jews). He would then give choice to the Jews that they have them (on their possession) by that assessment or could assign to them (Muslims) by that assignment, so that the (amount of) zakat could be calculated before the fruit became eatable and distributed (among the people).