I sold goods to one of them for 35 riyals, but he did not pay me the amount on the spot, so I said, "Then the price will be 40 riyals if the payment is delayed."

Question:
May Allah reward you, Honorable Shaykh. This questioner says: I sold goods to one of them for thirty-five riyals, but he did not pay me the amount on the spot, so I said, "Then the price of the goods will be forty riyals if the payment is made after three days." Is this arrangement valid?

Answer:
No, as long as you have sold it, it is not permissible for you to increase its price after the sale. This is not permissible as long as the contract has been completed; it is not permissible for you to increase the price after the sale. Because he said to you, "I have nothing right now, so wait for me," and you say, "I will not increase it for you." This is the riba of the pre-Islamic age of ignorance. This is the riba of the pre-Islamic age of ignorance. Yes.