Dr. Monzer Kahf, a prominent economist and counselor states: “currency exchange is permissible with two conditions: 1) the amount sold/purchased of both currencies must be delivered in full; and 2) delivery must be at the time of contract. It really doesn’t matter whether one trades on the internet or in a shop on a street corner as long as these two conditions are fulfilled. On the internet they can be fulfilled if delivery is done by debiting and crediting the account of the person for both amounts at the time of contract, this is what is called “al Qabdh”. This ruling came from a most authentic Saying of the Prophet, pbuh, that is reported by both Bukhari and Muslim.

Finally: the implication of the ruling is: 1) sale on margin is not permissible, futures in currencies are not permissible.”