Malik was asked whether the tenth or the twentieth was taken out of olives before they were sold or after and he said, "The sale is not taken into consideration. It is the people who produce the olives that are asked about the olives, just as it is the people who produce foodstuffs that are asked about it, and zakat is taken from them by what they say. Someone who gets five awsuq or more of olives from his olive trees has a tenth taken from the oil after pressing. Whereas someone who does not get five awsuq from his trees does not have to pay any zakat on the oil."
Malik said, "Someone who sells his crops when they are ripe and are ready in the husk has to pay zakat on them but the one who buys them does not. The sale of crops is not valid until they are ready in the husk and no longer need water."
Malik said, concerning the word of Allah the Exalted, "And give its due on the day of its harvesting," that it referred to zakat, and that he had heard people saying that.
Malik said, "If someone sells his garden or his land, on which are crops or fruit which have not yet ripened, then it is the buyer who has to pay the zakat. If, however, they have ripened, it is the seller who has to pay the zakat, unless paying the zakat is one of the conditions of the sale."
Arabic : Book 17, Hadith 613