If the term has not yet begun, he owes nothing; rather, he must return the property itself to its owner. But if part of the term has passed, he must return it to its owner and pay, in proportion to the period for which he used it, the customary rent.
His statement, “under an invalid lease,” means that a lease becomes invalid either through the absence of a condition or the presence of an impediment.
An example of the absence of a condition is when a man leases from someone a free person to work for him. It is known that leasing out a free person is not permissible, as stated in the authentic hadith: “A man who sells a free person and consumes his price” (1). Likewise, if he leases him out and consumes his wages, that is not lawful. Thus, for example, someone says to another: “Do you need a worker?” He replies: “Yes.” The first says: “This is my servant; take him for one month at one hundred riyals,” even though he is free. The lease here is invalid, because one cannot enter into a lease contract concerning a free person. One of the conditions of a lease is that the lessor own the leased property.
The lessee then takes this servant and employs him until the term ends. The author says that he—that is, the lessee—must pay the customary rent, because the lease contract was invalid, and what is invalid is treated as nonexistent. But how can the author say, “the customary rent,” when he is free and cannot validly be leased? We say: he is hypothetically regarded as though he were a slave—that is, an owned servant. It is then asked: “What would be the wage of this slave?” They say, for example: “His wage is two hundred riyals,” whereas he had been leased for one hundred riyals. We say: “Pay two hundred riyals,” because the stipulated wage is invalid. This applies when the lessee knows that this