A:
The transaction as described in the question
is a Riba (usury/interest)-bearing transaction and is thus unlawful. In fact, it is clear that the man who is to pay the deferred payment on your behalf expects to be repaid more than what he paid as he knows how much one-sixth of the profit equals. Moreover, your profits in selling the car you bought on credit is valid. Nevertheless, it is impermissible to pay back the man who lent you 5,000 riyals a larger amount of money and it is also impermissible for the lender to accept this profit. Rather, he should refrain from earning money through a usurious transaction, knowing that if he gives up something (unlawful) for the sake of Allah, He will replace it with something (even) better. (Part No. 11; Page No. 83) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.