—each item thereby becoming the price of the other, without any unfolding, scrutiny, or knowledge of its qualities. The two parties complete the purchase on those terms, with neither description nor prior inspection. The ruling whenever such a sale is concluded is that it must be rescinded in the manner already set out, unless the goods have vanished while in the buyer’s possession, in which case the judgment is as previously explained.

The same ruling applies to bayʿ al-ḥaṣāh (the pebble sale) that the Prophet—may Allah bless him and grant him peace—forbade. In this arrangement the buyer says to the seller, regarding a number of garments or similar items, “Whichever one my pebble lands on is mine for such-and-such a price,” and then he throws the pebble. This was a practice of the people of pre-Islamic times, and the Messenger of Allah—may Allah bless him and grant him peace—prohibited it because it contains elements of gambling, reckless risk-taking, and gharar, just as he forbade mulāmasa and munābadah. We have discussed all of this in detail in al-Tamhīd—praise be to Allah.

Among the transactions he likewise forbade is al-kāliʾ bil-kāliʾ, that is, one debt for another. This is a subject that is broad, ramified, and full of subsidiary issues within the school of Mālik and his companions. One such case is when a man is owed a sum by another—arising from a sale or a loan—and then buys from him a commodity on deferred payment. This is impermissible and must be annulled even after it has been concluded, because it is replacing one debt with another. If the commodity has already perished, it must be compensated at its value on the day it was taken into possession, except