Abu al-Jawza' narrates: I asked Sayyiduna Ibn Abbas (may Allah be pleased with them both) about sarf (currency exchange), about (selling) one dirham for two dirhams hand to hand, and he said: "I see no harm in whatever is hand to hand." Then I came to Makkah the following year, and he had forbidden it.
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 452