Is it permissible to purchase products in installments from a commercial company at the cash price, where promissory notes belonging to the company are signed, with the option of paying the company directly or paying the bank which deposits the amount into the company's account?

The prohibited aspect does not lie in the difference between immediate payment or deferred payment with an increase. Debt has a share of the price, and a company may sell its goods for a certain price for immediate payment and a higher price for deferred payment.

As long as the transaction is between the company and the customer, and the bank has no involvement in it, and the company sells goods to the customer at a specified and known price without imposing a penalty on him for late payment, then there is no harm in such a transaction, whether he pays the installments directly to the company or deposits them into its account with the bank.

However, it is necessary to ascertain and examine the terms and conditions of the transaction before entering into it.