Is it permissible for a mortgagee to pay a monthly rent for a house mortgaged to him, while the original amount remains unchanged? And if it is not permissible, what should he do with the received amounts?

The pledgor may benefit from the pledge in a way that does not diminish its value, such as riding an animal or residing in a house. If the benefit diminishes the value of the pledge, it is not permissible except with the permission of the pledgee. Others hold that the pledgor is not allowed to benefit from the pledged item except with the permission of the pledgee.

According to both opinions, it is not permissible for the pledgee (the merchant) to take a monthly rent for the man's residence in his house, because he does not own the house to rent it out, and this amount is considered forbidden usury (riba). The merchant must return what he has taken from this excess, and he is only entitled to the loaned amount.