His statement, “for the entire term, or part of it, he is entitled to nothing,” means that the lessor is entitled to nothing.
For example, he leases him this house for one year. When the lessee comes to claim it, he prevents him from taking possession of it, and the entire year passes while he has kept him from it. Is he entitled to rent? He is entitled to nothing, because he himself prevented him from it. But is he liable for the difference between the two rental values—namely, the market rent and the rent agreed upon in the contract—if they differ, or is he not liable?
For instance, if he leased it for ten thousand, but rents rose until, during that year, it became worth twenty thousand, must the lessor pay the lessee the difference, namely ten thousand?
The answer is that, according to the view adopted by the author, may Allah have mercy on him, we say: the lease has come to an end; the lessor is entitled to nothing, and the lessee owes nothing. According to the second view, however, he is liable, because the lease is not dissolved. The benefit belongs to the lessee from the time of the contract; thus, if the lessor prevents him from it, he is an unlawful usurper, and an unlawful usurper is liable for compensation.
If rental rates have fallen, is he liable for the reduction? No, because to say so would cause harm to the lessee. If the rent remains unchanged, then the matter is clear.
If he leases it to him for one year at twelve thousand, then prevents him from it for six months, after which he vacates the house for him and the lessee lives there for the remainder of the term, does the lessee owe anything? The author says that he owes nothing, because the lessor has deprived the lessee of the benefit of the house. The lessee may have intended to remain there for a full year.