What is the ruling on renting a shop or a house by paying an advance of 15,0 pounds and 100 pounds monthly, half of which (50 pounds) is deducted from the advance until it runs out, after which the full 100 pounds is paid, all without specifying a duration for the contract?

Answer:

This transaction, as described, is permissible, provided that the 15,0 pounds are considered an advance payment towards the rent, and not a loan given to the landlord for which the rent is then reduced. If it is an advance payment towards the rent, then it is permissible. The permissibility stems from the fact that the actual rent is 100 pounds per month. The tenant pays 50 pounds in cash and 50 pounds from the advance payment until the advance payment is depleted, after which the tenant pays the full 100 pounds in cash. This is a sound and permissible transaction. The key is that the 15,0 pounds are part of the rent and an advance payment for it, not a loan that benefits the lender (the tenant) by reducing the rent, as this would constitute riba (usury).

And Allah knows best.