lies a blatant infringement of the first seller’s right, and such aggression inevitably sows enmity and rancour among the Muslims.

A parallel instance is “buying over his purchase.” Imagine that someone has just sold a commodity for one hundred, when another man approaches the seller and says, “I will buy it from you for one hundred and twenty.” The seller then cancels the first contract and concludes a new one with the second buyer. This, too, is unlawful, for it is the purchasing counterpart of undercutting a sale.

Is the prohibition confined to the period of khiyār (the stipulated option to rescind) or is it absolute? The wording of the hadith is unrestricted: “It is not lawful for you to sell against your brother’s sale,” whether or not the option period is still in effect. Some jurists, however, interpret the ruling as limited to the time when the khiyār remains, arguing that once the option has expired the contract can no longer be revoked, or at the very least cannot be corrupted in the same way.

Consider the following example. A man sells another a car for 10,000 riyals and grants him a three-day option. A third party then goes to the buyer and says, “I will give you a better car for the same 10,000,” enticing him to return to the seller and announce, “I have cancelled the deal.” Or he approaches the seller instead and says, “I heard you sold your car to so-and-so for 10,000 riyals; I will pay you 11,000.” The seller cancels the first sale, refunds the money, and sells the car to the second man.

If, however, the three-day period has elapsed, some scholars hold that there is no objection: once the option has ended, a person may go to the buyer and offer, “I will sell you one like it for less,” or, “I will provide you with a better one for the same price you paid,” because the contract can no longer be annulled after the khiyār has expired.