Selling some Dirhams in cash for more Dirhams on credit
You are not entitled to take the profit you mentioned as it falls into the category of
selling some Dirhams with cash for more Dirhams on credit. This act is Haram (forbidden) and you are obliged to return the extra amount.
May Allah grant us success. May peace and blessings of Allah be upon our Prophet Muhammad, his family and Companions!