A man bought on installment and stipulated that if he paid regularly, a sum of one thousand riyals would be deducted from the price. What is the ruling?

Question:
He says: Honorable Shaykh, may Allah grant you success. A man bought goods from another man on monthly installments, and it was written in the contract: "If I pay regularly without delay, I am entitled to have a sum of one thousand riyals deducted from the price." Is this condition valid? And is the contract and the sale valid?

Answer:
If the other party agrees to the deduction, he has the right to deduct it if he wishes. He may even cancel the entire price; there is no objection. It is his right to cancel the whole or part of it; there is no objection. But the reverse is what is not permissible: saying that every time you delay, the amount increases and the installments increase. This is forbidden and not permissible. Yes.