Musnad Ahmad 27:363

Yazid narrated to us, Nafi‘ ibn ‘Umar informed us, from Abu Bakr—meaning Ibn Musa—who said: I was with Salim ibn ‘Abdullah ibn ‘Umar when a caravan belonging to Umm al-Banin passed by, which had bells with it. Salim narrated from his father, from the Prophet (peace and blessings of Allah be upon him), that he said: "The angels do not accompany a caravan that has a bell with it." [Salim then said:] "How many bells do you see among these?"