Musnad Ahmad 33:861

Mu'awiyah ibn 'Amr narrated to us, Za'idah narrated to us, from Husayn, from Salim ibn Abi al-Ja'd, Jabir ibn 'Abdullah narrated to us, he said: "While we were performing the Friday prayer with the Messenger of Allah, may Allah bless him and grant him peace, a caravan arrived carrying food." He said: "So they turned towards it until there remained with the Messenger of Allah, may Allah bless him and grant him peace, only twelve men. Then this verse was revealed: {And when they saw a transaction or a diversion, they rushed to it and left you standing} [Al-Jumu'ah: 11]."