Is it permissible for a bank to act as guarantor for the purchase of a machine, given the assumption of the possibility of adding interest to the mortgaged amount in the event of default in payment and delay in the sale of the property?

This transaction involves several prohibitions: dealing with a usurious bank without necessity, taking a fee for a guarantee which is purely a gratuitous contract, and the stipulated amount to be taken upon delay in selling the property is an interest-based increase, clearly prohibited. Therefore, this transaction is impermissible.