What is the ruling on differentiating the exchange rate of the dirham between cash and checks when transferring from Sudan to the UAE? Is this considered usury (riba)? And what is the ruling on working in exchange companies that deal in this manner?

It is not permissible to sell currency except through actual or constructive possession, and deferring possession in such transactions is invalid. The evidence for this is what was narrated by Al-Bukhari and Muslim that the Prophet, peace and blessings be upon him, said concerning currency exchange (sarf): "If it is hand-to-hand, there is no harm, but if it is deferred, it is not permissible." And in Muslim's wording: "What is hand-to-hand, there is no harm in it, but what is deferred is usury (riba)."

Likewise, it is stated in Sahih Muslim that the Prophet, peace and blessings be upon him, forbade exchanging silver for silver, and gold for gold, unless it was equal for equal. He also commanded that silver be bought with gold, and gold with silver, as we wish, hand-to-hand.

Therefore, exchanging currency with a deferred check is not permissible. However, exchanging cash with an increased exchange rate when the currencies differ is permissible. Working in currency exchange offices is permissible in principle, but it is not permissible for an employee to directly engage in forbidden transactions or assist in them.