silver for silver except in equal quantities; do not sell wheat for wheat except in equal quantities; do not sell barley for barley except in equal quantities; do not sell dates for dates except in equal quantities; and do not sell salt for salt except in equal quantities.”

He, may Allah bless him and grant him peace, also prohibited selling a heap of foodstuffs of unknown volume in exchange for a specified measure of foodstuffs. Thus, these commodities may not be exchanged for others of the same kind without measuring their quantities, because the Prophet, may Allah bless him and grant him peace, prohibited exchanging them except in equal quantities. If their equality is not established, the sale is impermissible. Hence the jurists say:

“Not knowing whether the quantities are equal is like knowing that they are unequal.”

Equality is established by measuring volume or weight. Estimation, by contrast, is a matter of conjecture and approximation, used when there is need or necessity, but not when measurement by volume or weight is possible. The Prophet, may Allah bless him and grant him peace, therefore prohibited muhāqalah and muzābanah because people were estimating quantities without any need to do so. He permitted this in ‘arāyā sales because of need: the buyer needs fresh dates to eat and exchanges dried dates for them on the basis of an estimate to meet that need. He allowed this concession for the small quantity needed, below the prescribed threshold—that is, less than five wasqs. It is likewise permissible when the seller needs to sell, as has been explained at length elsewhere.

The linguistic meaning of “‘arāyā” is date palms that a man lends to someone else: he gives them to him so that he may eat their fruit, then return them to him, as the poet said in praise of a man’s generosity: