Musnad Ahmad 448:6

Yahya ibn Ishaq narrated to us, he said: Ibn Lahi'ah narrated to us, from 'Ayyash ibn 'Abbas, from Shuyaym ibn Baitan, he said: Maslamah ibn Mukhallad was over the lower land, he said: So he employed Ruwayfi' ibn Thabit al-Ansari, and we traveled with him from Sharik to Kawm 'Alqam, or from Kawm 'Alqam to Sharik. He said: Then Ruwayfi' ibn Thabit said: We used to go on military expeditions during the time of the Messenger of Allah, peace and blessings of Allah be upon him, and one of us would take his brother’s camel on the condition that he would have half of what he gained as spoils. He said: To the extent that one of us would be allotted the arrow shaft, and the other the arrowhead and the feathers. He said: Then Ruwayfi' ibn Thabit said: The Messenger of Allah, peace and blessings of Allah be upon him, said to me: "O Ruwayfi', perhaps life will be long for you, so inform the people that whoever knots his beard, or hangs a bowstring around his neck, or cleans himself (after relieving himself) with the dung of an animal or a bone, then he is free from what Allah revealed to Muhammad, peace and blessings of Allah be upon him."