Is buying dollars from Libyan banks and later selling them on the black market considered usury (riba)? And is it permissible to sell dollars at the prevailing black market rate?

For the exchange of currencies with one another, it is a condition that possession be taken in the مجلس (session or gathering), either actually or constructively. Constructive possession is achieved by the bank recording a sum of money in the client's account, and by receiving a check if it has a withdrawable balance. If the bank deposits the dollars into the account in the same session but they cannot be withdrawn until after a period due to reasons beyond control, then the currency exchange is valid. However, it is not permissible to dispose of the dollars until they can be actually taken. But if the bank does not deposit the dollars into the account in the same session, then this is usurious and forbidden currency exchange. It is not permissible to sell the right to receive dollars (selling a debt) to merchants for less than the recorded amount, as this is forbidden usury. Whoever owns the dollars or withdraws them, it is permissible for him to sell them for local currency or other currencies, provided that possession is taken in the مجلس, even if at a price higher than the official rate.