What is the ruling on adding an amount of (2000) Saudi Riyals to the value of a contract for selling (5) mobile phones in installments for a total amount of (5000) Riyals, knowing that there is a clause in the contract indicating that this amount will be discounted upon regular payment, but it is only applied in cases of severe procrastination?

This condition is forbidden and is a form of usury, because the reality of the contract is that the price is 5000, and if payment is delayed, a penalty of 2000 is paid. This increase in debts in exchange for delayed payment is among the usury forbidden by consensus. Furthermore, the lack of true knowledge of the price invalidates the sale and makes it unlawful, due to the Prophet's (peace be upon him) prohibition of gharar (uncertain or risky) sales.