Musnad Ahmad 33:67

'Abd al-Wahhab narrated to us, Sa'id narrated to us, from Matar, from Muhammad ibn Sirin, that Dhakwan Abu Salih—and he praised him well—narrated from Jabir ibn 'Abdullah, Abu Sa'id, and Abu Hurayrah, that they: "Forbade *al-sarf* (the exchange of gold and silver/currency exchange)." Two of them attributed it to the Messenger of Allah, may Allah bless him and grant him peace.