some measured goods be sold for other measured goods by estimation, nor weighed goods for other weighed goods by estimation. This is because their equality must be known, and ignorance of equality is like knowing that there is disparity. That is, even if we were to bring a skilled estimator who said, “This heap of wheat is equal to this heap of wheat,” it would still not be permissible to exchange them, because equality must be established through measurement by volume—except for one case that will come, Allah willing: al-ʿarāyā sales, which may be conducted on the basis of estimation.

His statement, “Nor may some of it be sold for some of it by estimation”: if some of it is sold for some of it by estimation, then before taking possession each party measures by volume what has come to him and finds it equal to the other, the contract is valid, because the prohibition has been removed and there is no longer any ignorance. The commodity sold is known to both parties; the issue was only its standard of measurement, and we now know that the two are equal according to the legal standard.

His statement, “If the kinds differ, all three are permissible”: if the kinds of the two commodities differ—for example, if wheat is sold for barley—then all three methods are permissible: selling by volume, by weight, or by estimation.

The reason for this permissibility is that when a ribā commodity is sold for something other than its own kind, disparity is permitted.

For example, one purchases barley with wheat: a kilogram of wheat for a kilogram of barley. This is permissible because they are of different kinds. When the kinds differ, the Prophet (peace and blessings be upon him) said: “When these kinds differ, then sell as you wish, so long as it is hand to hand” (1). Likewise, if barley is sold for dates by weight—one kilogram of this for a kilogram of