Musnad Ahmad 1273:15

Hashim narrated to us, Al-Layth—meaning Ibn Sa'd—narrated to us, Nafi' narrated to me, from Salim ibn 'Abdullah, from Al-Jarrah, the freed slave of Umm Habibah, the wife of the Prophet, may Allah bless him and grant him peace, that he heard him informing 'Abdullah ibn 'Umar that Umm Habibah narrated to him that the Messenger of Allah, may Allah bless him and grant him peace, said: "The caravan that has a bell with it, the angels do not accompany it."