Is it permissible to sell a commodity for cash and then sell it in installments at a higher price, with the price remaining fixed whether payment is made early or late?

There is no harm in selling by installments with an increase over the cash price, such as selling an item worth ten thousand for ten thousand five hundred in installments over two months, provided that the price does not change and no late payment penalty is imposed, because in this case, the increase or penalty is considered prohibited usury (riba).