Musnad Abu Ya'la al-Mawsili 108:150

Zuhayr narrated to us, 'Abbad ibn al-'Awwam narrated to us, Hajjaj informed us, from Abu al-Zubayr, from Jabir, who said: We used to not kill the merchants of the polytheists during the time of the Messenger of Allah, may Allah bless him and grant him peace.