If after the end of the rental period it becomes apparent that the rental agreement was invalid, the lessee must pay the owner of the property the standard rate for that property (ujrat al‑mithl). For example, if a person gives a house on rent for a year for £10,000 and later finds out that the rental agreement was invalid, in the event that the rent for that house is normally £5,000, the lessee must pay him £5,000.
And if the standard rate is £20,000, in the event that the lessor was the owner of the property or an agent who had the authority to specify the rent and knew the normal price of the house, it is not necessary for the lessee to pay more than £10,000; otherwise, he must pay £20,000. Furthermore, if after the passing of some of the rental period it becomes apparent that the rental agreement was invalid, the same rule (ḥukm) applies to the fee in relation to the period that has passed.