From Islamic Finance WIKI
Sarf is the exchange of money. The rulings of exchange of fiat money are based on the rules of exchange between the six classic monetary items gold, silver, wheat, barley, salt and dates.
The basic conditions are the absence of delay (nasi'a) and the absence of excess (tafadul) according to Ibn Rushd with the objective to avoid Riba and Gharar. Currency dealings are executed on a spot basis, and for equal countervalues. The funds to be exchanged can be in the form of cash, cheques, or transfers over account. A fee may be charged by the party exchanging the funds.
Currency dealings are not subject to forward sales contracts although a unilateral binding promise might be used to structure financial products which have forward type characteristics. Scholars tend to permit these contracts provided they are used for hedging and not for speculative putposes.
- Islamic Forex Trading by Dr Mohammed Obaidullah