"The Prophet of Allah (ﷺ) would clean his teeth with the Siwak, then he would give me the Siwak in order to wash it. So I would first use it myself, then wash it and return it.
Sunan Abi Dawud Book 1, Hadith 52
← Previous Hadith "What would the Messenger of Allah (ﷺ) do as soon as he entered the house?" She replied: "(He would use) the siwak."

Sunan Abi Dawud Book 1, Hadith 51 Next Hadith → The Messenger of Allah (ﷺ) said: Ten are the acts according to fitrah (nature): clipping the moustache, letting the beard grow, using the tooth-stick, cleansing the nose (Al-Istinshaq) with water, cutting the nails, washing the finger joints, plucking the hair under the arm-pits, shaving the pubes, and cleansing one's private parts (after easing or urinating) with water. The narrator said: I have forgotten the tenth, but it may have been rinsing the mouth.

Sunan Abi Dawud Book 1, Hadith 53