Musnad Ahmad 32:519

'Abd al-Samad narrated to us, my father narrated to us, and 'Affan narrated to us, 'Abd al-Warith narrated to us, Shu'ayb—meaning Ibn al-Habhab—narrated to us, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "I have spoken to you excessively regarding the siwak (tooth-stick)."