the two wages is that, if the worker agrees, the payment belongs to the first person who hired him. For example, if he brought him over on a monthly salary of three hundred riyals—that is, ten riyals per day—and then, with his permission, hired him out for fifteen riyals per day, the additional five riyals belong to the one who first hired him. This is because the worker agreed to work for someone else, while the first hirer owns his benefit. But if he refuses and says, “No, I will not work for anyone other than you unless you give me the difference between your wage and the other person’s wage,” then he is free and entitled to stipulate this.
His statement: “and teaching a field of knowledge,” meaning that a person hires someone to teach him a chapter from one of the fields of knowledge—for example, hiring someone to teach him the chapter on purification or the chapter on leasing. This is permissible, but the particular field of knowledge must be specified.
If someone were to say: The benefit here may be impossible to define, because you do not know when this man will learn. Some people are quick to understand and memorize, and slow to forget, so they learn quickly. Others are the opposite: you teach them repeatedly, make matters clear to them, explain to them using the board and every possible method, yet they still do not understand. So how can hiring someone to teach knowledge be valid? We reply: this is one of the matters in which some latitude is allowed, and it is assessed according to the average person—not one who is quick to understand, memorize, and retain, nor one who is slow. Rather, it is determined by customary practice.
His statement, “and teaching a field of knowledge,” is not unrestricted. For it will come later that it is not permissible to teach forbidden fields of knowledge, nor to hire someone in order to learn them. It is also not unrestricted for another reason: among the best branches of knowledge is the Quran, yet the jurists stated that it is not valid to hire someone to teach the Quran, because