Must the debt being assigned be a firmly established and liquid debt?
General Chapter
Al-Mughni
Book of Assignment (Transfer of Debt)
Primary text
The second condition is that the debt must be firmly established. Assignment is not permitted for an unascertained debt. Specifically, a Salam contract (forward sale) cannot be the subject of assignment either to or from the seller, because the Salam debt is not firm due to the possibility of nullification if the subject matter becomes unavailable. Assignment is also invalid for the stipulated payment of a Mukatab (a slave purchasing his freedom), because this debt is not firm as the Mukatab may refrain from paying or his inability may nullify it. However, assignment is valid concerning any debt owed by the Mukatab other than the writing payment, as in commercial transactions, he is treated as a free person. If the Mukatab assigns his master for an installment due, it is valid, and the Mukatab's liability is discharged, which functions as immediate fulfillment.
Supporting text
If a woman assigns her dower debt to her husband before consummation, it is invalid because it is not firm. If the husband assigns it to her, it is valid, as his assignment constitutes immediate delivery. If she assigns it after consummation, it is valid because it is firm. If the seller assigns the purchase price against the buyer during the option period, it is invalid based on established analogy, but if the buyer assigns the price to the seller, it is valid as it is equivalent to fulfillment. If the seller assigns the price, and later a defect in the sold item is discovered, one opinion holds the assignment is not voided because the price was firm at the time, while another suggests it is voided because the defect existed at the time of assignment. If the non-firm debt is extinguished (e.g., divorce or rescission of sale) before the assigned party fulfills the obligation, there are two views: one, the assignment is voided as it becomes pointless, and the assignor reverts to the assigned party; the second, it is not voided because the right transferred from the assignor and was established for the assignee, treating the assignment as fulfillment. If extinguishment occurs after fulfillment, it is universally not voided, and the assignor reverts to the assignee.