As soon as palm trees and grapevines ripen and their produce is ready to be picked, an estimation of their nisab is made without their actual weighing. The process is carried out by a knowledgeable and trustworthy person who estimates the amount of fresh grapes and dates still on the trees for zakah as if they were dry dates and raisins. The amount of zakah is, however, payable when the fruit becomes dry.
Abu Humayd as-Sa’idi related: “We went on the expedition of Tabuk with the Prophet, upon whom be peace. When we arrived at Wadi al-Qura, we saw a woman in her orchard. The Prophet said: ‘Let us estimate [her zakah].’ Then the Messenger, upon whom be peace, estimated ten awsuq and told her: ‘[The amount of zakah] has been calculated on your [orchard’s] produce.'” This is narrated by alBukhari.
This is the practice of the Messenger of Allah, upon whom be peace, and his companions and the scholars observed it.
The Hanafiyyah have different views because they consider conjecture to be uncertain, and therefore, of no use in determining the amount owed. Still, the tradition of the Messenger of Allah is a better guide (‘azha) because conjecture is not guessing; it is a diligent attempt to estimate the amount of the produce. It is the same as estimating the amount of the produce lost (because of its being rotten or moth-ridden). The basis for conjecture rests on the custom that people eat fresh fruits, and as such, there is no need for calculating the amount of zakah before it is eaten or plucked. In this way, the owners are allowed to do what they want and, at the same time, to determine the amount of zakah. The appraiser should ignore a third or a fourth of the produce as a reprieve for the property owners since they, their guests, and their neighbours need to eat some of it. Also, the produce is exposed to such perils as birds feeding, passers-by plucking, and wind blowing. Any appraisal of the amount of zakah on all of the produce without excluding a third or a fourth of it (for the preceding reasons) would have militated against the genuine interests of the owners.
Sahl ibn Abu Hathamah related that the Prophet, upon whom be peace, said: “Whenever you conjecture, estimate the [zakah] and ignore one-third. If you do not, then leave [at least] one-fourth.” This is narrated by Ahmad and the authors of Sunan, except for Ibn Majah. It was also reported by al-Hakim and Ibn Hibban, and they both authenticated it. Commenting on the status of the report, atTirmizhi says: “The hadith reported by Sahl is the one enacted or followed by most scholars.” Bashir ibn Yassar said: “When ‘Umar ibn al-Khattab appointed Abu Hathamah al-Ansari to estimate the property of Muslims, he told him: ‘Whenever you see that the people have left some dates unplucked for autumn, leave them for the people to eat, and do not estimate the zakah on them.’ “
Makhul said: “Whenever the Messenger of Allah, upon whom be peace, assigned someone to estimate, he would say: ‘Be easy on the people, for some of their property [trees] could be barren, some low, and some for [their] eating.'” It was narrated by Abu ‘Ubaid, who added: “The low palm tree is called as-sabilah and allows its fruit to be plucked by passers-by. The eating tree (al-akilah) is a palm tree especially designated as an eating tree for the owner’s family or for whoever is attached to them.”