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 Muslim in the book of purification (254), both from the hadith of Hammad bin Zayd, from Ghaylan bin Jareer, from Abu Burda, from his father, who narrated it as mentioned. This is the wording of Bukhari. The wording of Muslim is, "I came in to see the Prophet ﷺ while the tip of the siwak was on his tongue, retching."The word "yatahawwau" comes from tahawwu, which means vomiting. It is said "haa yahuu huwaan" when someone vomits. What is meant here is the drawing up of phlegm from the back of the throat and bringing it out to spit it, which is what someone does when they want to vomit.