A person asked me to buy a car for him for cash, and then sell it to him on installments with an increase in the price. What is the ruling on this transaction?

Question:
May Allah reward you with good and do you well. If a person asks me to buy a specific car for him for cash, and then I sell it to him on installments with an increase in the price—for example, I buy it for fifty thousand riyals and sell it to him on installments for seventy thousand riyals—is this transaction lawful or forbidden? May Allah reward you with good.

Answer:
If the car or the commodity you want to sell at a deferred price is in your possession before the contract with the borrower, meaning you own it before you make the contract with the borrower, then there is no harm in that, and this is a lawful sale. However, if it is not in your possession, and the contract is made first and then you go and buy it, this is forbidden. The Messenger of Allah (peace and blessings be upon him) said: "Do not sell what you do not have." Yes.