Musnad Abu Ya'la al-Mawsili 155:217

Abdullah ibn Umar ibn Aban narrated to us, Yahya ibn Yaman narrated to us, from Hisham, from Muhammad ibn Sirin, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) forbade *al-sarf* (the exchange of currency), a dirham for two dirhams, and Abu Bakr, Umar, and Uthman [did the same].