What is the ruling on the sale of one heap (*ṣabrah*) of a commodity for another heap of the same commodity when their measures are unknown?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
If one states, 'I sell you this heap for this heap,' and both are of the same genus but their measures are unknown, the sale is invalid due to the lack of the required equivalence. If their measures are known and found to be equal, the sale is valid because the stipulated equivalence is met. If one states, 'I sell you this heap for this heap, like for like,' and upon measuring they are equal, the sale is valid; otherwise, it is void.
Supporting text
If one sells a heap for a heap of a different genus, the sale is valid according to those who permit the sale of measured goods for measured goods by estimation. If equality is stipulated ('like for like'), and they are found equal, the sale is valid. If one is larger and the owner of the deficient one accepts it with its deficiency, or the owner of the excess agrees to return the surplus, it is permissible; otherwise, the sale must be annulled.