It is possible that al-Nakha'i stated this based on his school of thought, in which one who leases something may not re-lease it for an increase. The analogy of the school of thought is the permissibility of that, regardless of whether he assisted in it with anything or did not; for if it is permissible for him to subcontract it for the equivalent of the first rent or less, it is permissible for more than it, like a sale and like the leasing of an asset.

Section: Every asset that one leases for a benefit, he is permitted to utilize a benefit similar to that one, or one that is less in terms of damage. Ahmad said: If one leases a beast to carry dates upon it, but carries wheat instead, I hope there is no harm in that, provided the weight is the same. If the benefit he utilizes is more damaging, or differs from what was contracted in terms of damage, it is not permissible, because he is utilizing more than his right, or something other than what he is entitled to. Thus, if he rents a beast to carry iron, he must not carry cotton on it, because it shifts and the wind blows through it, which tires the back. If he rents it to carry cotton, he is not permitted to carry iron, because it collects in one place, which weighs heavily on it, whereas cotton disperses, thus its damage is less. If he rents it to ride, he is not permitted to carry a load on it, because the rider assists the back with his movement. If he rents it to carry a load, he is not permitted to ride it, because the rider sits in one place, which presses hard on the back, while luggage distributes across its sides. If he rents it to ride bareback, he is not permitted to ride it with a saddle, because he would be loading it with more than he contracted for. If he rents it to ride with a saddle, he is not permitted to ride it bareback, because when he rides it without a saddle, its back heats up, and he might cause it injury. If he rents it to ride with a saddle, he is not permitted to ride it with anything heavier. Thus, if he rents a donkey with a saddle, he is not permitted to ride it with a pack-mule's saddle, if it is heavier than its own saddle. If he rents a beast with a saddle and rides it with a pack-saddle that is heavier or more damaging, it is not permissible; but if it is lighter and less damaging, there is no harm. Whenever he does what he is not permitted to do, he is a guarantor and liable for the rent. This is the entire position of al-Shafi'i and Abu Thawr.