Could you mention a summary of the rulings on Al-Ja'alah?

A ju'alah (reward/stipend) is what is given to a person in exchange for work they perform, such as saying, "Whoever does such-and-such will receive such-and-such amount of money." Evidence for its permissibility from the Qur'an is the Almighty's saying: (And for he who brings it [there shall be] a camel's load; and I am guarantor of it) Yusuf/72. From the Sunnah, there is the hadith of the stung person. The reward is due to whoever performs the work after being informed of it. If a group performs it, they share it. The ju'alah is a permissible contract for both parties. If the termination is from the worker, he is not entitled to anything. If it is from the one offering the reward, and before the work has commenced, the worker is entitled to a fair wage for his work. Ju'alah differs from ijarah (leasing/hiring) in several aspects, including not requiring knowledge of the work or its duration, the possibility of combining work and duration, the worker not being bound, and the permissibility of terminating the contract. Whoever performs work for another without a reward or permission is not entitled to anything, except for someone who has prepared themselves to work for a wage, like a broker, or someone who saves another's property from destruction, in which case they are entitled to a fair wage.