What are the conditions for the validity of a Ja'alah contract regarding the specification of the work and the reward?
General Chapter
Al-Mughni
Book of Lost-and-Found Property
Primary text
If someone states, 'Whoever returns my lost property or runaway slave, or sews this shirt for me, or builds this wall for me, shall have such and such reward,' the contract is valid and considered a permissible contract where either party may withdraw before the work is completed. If the giver withdraws before the worker commences the task, he owes nothing. If the giver withdraws after the work has commenced, he owes the worker the customary wage (ujrat mithl) for the labor performed, as the worker acted in expectation of compensation. If the worker terminates before completing the work, he forfeits any claim because he abandoned his right by failing to fulfill the condition for receiving compensation. The reward (iwad) must be known. The reward must be known because while the need calls for the work itself to be unspecified (due to unknown location of lost items), there is no corresponding need for the compensation to be unknown, and since the compensation becomes binding upon completion of the work, it must be specified.
Supporting text
A probability exists that Ja'alah is valid even with an unknown reward if the uncertainty does not prevent delivery, such as saying, 'Whoever returns my runaway slave shall have half of him,' or 'Whoever returns my lost property shall have a third of it.' Imam Ahmad permitted a general reward set by a commander in campaign, like giving one head of livestock for bringing ten. It is also likely permissible if the unknown reward is derived from the property of the disbelievers, like specifying a female slave to be brought by the worker, from which a similar item is then given. However, if the uncertainty prevents delivery, the Ja'alah contract is invalid by unanimous agreement.