Maliks Muwatta Book 31, Hadith Number 49.
Yahya related to me from Malik from Nafi that Abdullah ibn Umar said that there was no harm in a man making an advance to another man for food, with a set description and price until a set date, as long as it was not in crops, or dates which had not begun to ripen.
Malik said, “The way of doing things among us concerning someone who makes an advance for foodstuffs at a known rate until a stated date, and the date arrives and he finds that there is not enough of what he was sold with the seller to fulfil his order, and so he revokes the sale, is that he must only take back the silver, gold, or price which he paid exactly. He does not buy anything else from the man for the same price until he has got back what he paid. That is because if he took something else besides the price which he paid him or exchanged it for goods other than the goods which he bought from him, it would be selling food before getting delivery of it.”
Malik said, “The Messenger of Allah, may Allah bless him and grant him peace, forbade selling food before getting delivery of it.”
Malik said that it was not good if the buyer regretted his purchase and asked the seller to revoke the sale for him and he would not press him immediately for what he had paid. The people of knowledge forbade that. That was because when the food was made ready for the buyer by the seller, the buyer deferred his due from the seller in order that he might revoke the sale for him. That was the sale of food with delayed terms before taking delivery of the food.
Malik said, “The explanation of that is that when the date of delivery comes and the buyer dislikes the food, the seller takes by it money to be paid later and so it is not revocation. Revocation is that in which neither the buyer nor the seller is increased. When increase occurs by deferment of payment for a time period, or by anything which increases one of them over the other or anything which gives one of them profit, it is not revocation. When either of them do that, revocation becomes a sale. There is an indulgence for revocation, partnership, and transfer, as long as increase, decrease, or deferment does not come into them. If increase, decrease, or deferment comes into it, it becomes a sale. Whatever makes a sale halal makes it halal and whatever makes a sale haram makes it haram.”
Malik said, “If someone pays in advance for Syrian wheat, there is no harm if he takes a load after the term falls due.”
Malik said, “It is the same with whoever advances for any kind of thing. There is no harm in him taking better than whatever he has made an advance for or worse than it after the agreed delivery date. The explanation of that is that if, for instance, a man advances for a certain weight of wheat. There is no harm if he decides to take some barley or Syrian wheat. If he has made an advance for good dates, there is no harm if he decides to take poor quality dates. If he paid in advance for red raisins, there is no harm if he takes black ones, when it happens after the agreed delivery date, and when the measure of what he takes is like the measure of what he paid for in advance.”