Musnad Ahmad 945:0

Narrated by Abu Bashir al-Ansari: He was with the Messenger of Allah (ﷺ) on one of his journeys. The Messenger of Allah (ﷺ) sent a messenger to the people, saying: "There shall not remain a necklace of string or any other type of necklace around the necks of camels, except that it must be cut." Ibn 'Awn said: I think he said: "Or a bowstring."