Sayyiduna Bara' and Sayyiduna Zayd bin Arqam (may Allah be pleased with them both) narrate: The Prophet (peace and blessings be upon him) arrived while we were engaged in sarf (currency exchange), and he (peace and blessings be upon him) said: "There is no harm in it hand to hand," but he disliked (it on) credit.
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5020