I came to the Messenger of Allah ﷺ while he was cleaning his teeth with a siwak in his hand, saying, "Ugh, ugh," with the siwak in his mouth, as if he were gagging.
أتيت رسول الله ﷺ وهو يستن بسواك بيده، ويقول: أع أع والسواك في فيه، كأنه يتهوع.
Bukhari narrated it in the book of wudu (244), and this is his wording, and Muslim in the book of purification (254), both of them from the hadith of Hammad bin Zayd, from Ghaylan bin Jareer, from Abu Burda, from his father.Muslim's wording states, he said, "I entered upon the Prophet ﷺ while the end of the tooth-stick was on his tongue."His saying "yatahawwa" comes from tahawwu, which means vomiting. It is said, "haa yahoo huwaan," when someone vomits. What is meant here is bringing up phlegm from the back of the throat and expelling it so as to spit it out, which is what someone does when they want to vomit.