Musnad Abu Ya'la al-Mawsili 108:121

Zuhayr ibn Harb narrated to us, Jarir ibn Abd al-Hamid narrated to us, from Husayn, from Salim, from Jabir: That the Prophet, peace and blessings of Allah be upon him, was delivering the sermon standing on the day of Friday. Then a caravan came from Ash-Sham, and the people turned away until there remained only twelve men. Then this verse which is in [Surat] al-Jumu'ah was revealed: "And when they see a transaction or a diversion, they disperse to it and leave you standing."