What do the respected scholars and senior muftis say about the following issue that a man came to me and said, “I need 15,000 rupees cash from you and I will pay you a profit of 2,000 rupees.” I replied that I could not do that directly, but I could buy goods worth 15,000 rupees on his behalf. Then we both went to a shop; in his presence I bought an engine from the shopkeeper for 15,000 rupees and paid the shopkeeper either immediately or later. After the engine became my property, I sold that same engine to the man for 17,000 rupees and handed it over to him. I told him that it is now up to him whether he wants to sell it back to that shopkeeper or to someone else; he may pay me the 17,000 rupees in monthly installments. Now the question is: according to Shariah, is the described method valid or not? A simple answer is required please explain in detail.
If this method is not used as a pretext to make an interest-based transaction permissible, then conducting the transaction in the manner mentioned is undoubtedly lawful and valid. However, if any installment is delayed for some reason, it is necessary to refrain from charging any additional penalty or fine.