What is the ruling when the sale of oil is set per unit weight (per ratl), contingent upon weighing the container afterward to calculate the final price based on the oil's actual weight?
Chapter on Selling Assets and Fruits
Al-Mughni
Book of Sales
Primary text
If the sale is structured such that the price per ratl applies to the oil, and the container's weight is determined afterward to calculate the total price based on the oil's weight, the transaction is valid, provided both parties know the weights of both the oil and the container beforehand. For example, if it is known that the oil is ten ratls and the container is one ratl, this implies a sale of ten ratls of oil for twelve dirhams (if the price per ratl is one dirham).
Supporting text
If the parties are ignorant of the weight of both the oil and the container, the sale is invalid. This invalidity results from the potential for ambiguity in the final price at the moment of contract formation. The ruling applies equally whether they are ignorant of both weights or only one of them.