Is it permissible to undergo a surgical operation by installments with an increase in cost?

If the contract was initially made on the basis of installment payments for the rent, then there is no harm in that, even if the deferred rent is more than the immediate rent, because the deferment has a share in the price. Ijara (leasing/renting) is divided into two types: ijara related to a specific object (‘ayn), and ijara related to a liability (dhimma). Ijara related to a specific object does not require the rent to be paid in the session (of contract), because it is like selling a specific object, which is valid with both immediate and deferred payment. As for ijara related to a liability, scholars have differed on the obligation of paying the rent in the contract session. The difference is not due to the increase for deferment, but rather because both the benefit and the rent are in the form of a liability.