Musnad Ahmad 31:63

'Abd al-Wahhab al-Khaffaf narrated to us, Sa'id narrated to us, from Matar, from Muhammad ibn Sirin, that Dhakwan Abu Salih—and he praised him with good—narrated from Jabir ibn 'Abdullah, Abu Sa'id al-Khudri, and Abu Hurayrah: That they forbade *al-sarf* (the exchange of gold for gold or silver for silver with a difference in weight or delay). Two men among them attributed it to the Messenger of Allah, may Allah bless him and grant him peace.