Is it permissible for me to sell my car to my friend on condition that he sells his car to another friend of mine, knowing that both sales will be by mutual agreement and in installments for both cars, with a price reduction in return for helping the friend?

Scholars have differed on the permissibility of stipulating one contract within another, holding three opinions: absolute prohibition, which is the view of the majority; prohibition with the exception of certain contracts, which is the view of the Malikis; and absolute permissibility, which is the view of Ibn Taymiyyah and Ibn al-Qayyim.

Those who prohibit it cite the hadith (definition): "The Messenger of Allah, peace and blessings be upon him, forbade two sales in one sale," interpreting it as stipulating one contract within another. Whereas those who permit it interpreted the hadith as referring to Bay' al-Inah (a type of buy-back sale).

Those who permit it argue that the default rule for contracts and conditions is permissibility, unless there is evidence to prove its prohibition, relying on the hadith: "Muslims are bound by their conditions."

The most preponderant opinion is the permissibility of stipulating one contract within another, as long as it is not a ruse for Riba (usury) or involves a loan that brings benefit. Therefore, there is no harm in selling your car on the condition that the buyer sells his car to your friend.