What is the third condition for a valid assignment of debt regarding the subject matter?
General Chapter
Al-Mughni
Book of Assignment (Transfer of Debt)
Primary text
The third condition is that the assignment must be for a known quantity, because if it were a sale, it would be invalid for the unknown, and if it is a transfer of right, specification is required for fulfillment. Thus, it is valid for anything that establishes a debt through destruction, such as currency, grains, or oils, but not for that which is invalid in a Salam contract because it does not establish a debt. There is a difference of opinion regarding assignment for non-fungible items whose like establishes a debt in a Salam contract, such as measured cloth or counted items. One view holds it is invalid because the like cannot be determined, thus it is not guaranteed by its like upon destruction, which is the apparent view of the Shafi'i school. The second view holds it is valid because it is an established right in the liability, similar to fungible property.
Supporting text
These two views might stem from the disagreement over what necessitates a loan for these properties. For instance, if the debt is camels from blood money, and the assigned debt is similar camels in age, one opinion holds it is valid, defining equivalence by the minimum age and characteristics. Another opinion holds it invalid due to uncertainty and because camels are not fungible items guaranteed by their like upon destruction. If the debt owed is similar camels as a loan, and the assignment is accepted, if the loan requires repayment of value, the assignment is invalid due to different genus; if it requires the like, the assignment is valid because the right can be fulfilled according to its nature from the assigned party, who agreed to discharge with what he owes the borrower.