What is the ruling on a sale in which the merchant sets three different prices for each commodity based on the payment period, given that the commodity is present and can be taken without prior payment?

It is permissible to sell a commodity for a deferred price that is higher than its cash price, whether the deferment is for a single period or multiple periods, provided that an agreement is made on a specific single period to determine the price, and that the seller does not stipulate an increase in the price if there is a delay in paying the installments.