And whoever sells adulterated goods is forbidden to retain only the portion of the price attributable to the adulteration. He must return it to its owner or, if returning it proves impossible, give it in charity on his behalf. For example, someone sells a defective, adulterated item for ten dirhams; it would be worth ten if sound, but with the defect it is worth eight. If he knows the buyer, he must pay him the two dirhams if the buyer chooses this; otherwise, the buyer returns the purchased item to him. If he does not know the buyer, he must give the two dirhams in charity on his behalf. And Allah knows best.

He—may Allah have mercy on him—was asked:

“Some people make cloaks using unusable wool that they call ‘sallāqa.’ They fraudulently mix it with flax tow and sell it as good-quality wool. A merchant may know about this, but conceal it from the buyer. What must the manufacturer do? Is it permissible to trade in such goods while concealing this from the buyer? What is the ruling on manufacturing them in the first place? What must Muslims who have done this do? And what must those in authority do about people who mix flax tow into white wool and repeatedly return to this practice despite having been forbidden to do so more than once?”

He replied:

Praise be to Allah. The manufacturer may not make this, nor may the seller sell it, even if the buyer knows that it has a defect, because the degree of adulteration is unknown. It is reported of the Prophet, may Allah bless him and grant him peace, that “he prohibited mixing