This is a kind of selling dirhams in cash in return for more dirhams that will be paid at a definite time in the future. This is called Riba Al-Nasi'ah (usury of delay, conditional excess for delay of payment) and Riba Al-Fadl (usury of excess, selling an item for another of the same type, on the spot, but in excess). The Qur'an and the Sunnah point out that these two kinds of Riba are prohibited. Therefore, it is not permissible to exchange four thousand Dirhams in cash for six thousand Dirhams that will be paid at a certain time in the future. The seller should not receive anything more than his capital which is four thousand riyals. (Part No. 13; Page No. 332) If you dispute in this regard, you have to refer to the court. You should also repent to Allah and seek His forgiveness for this major sin. Allah (Exalted be He) says,
And all of you beg Allâh to forgive you all, O believers, that you may be successful
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.