Whenever the Prophet (ﷺ) got up at night, he used to clean his mouth with Siwak.
Sahih al-Bukhari Book 4, Hadith 111
← Previous Hadith My father said, "I came to the Prophet (ﷺ) and saw him carrying a Siwak in his hand and cleansing his teeth, saying, 'U' U'," as if he was retching while the Siwak was in his mouth."

Sahih al-Bukhari Book 4, Hadith 110 Next Hadith → The Prophet (ﷺ) said, "I dreamt that I was cleaning my teeth with a Siwak and two persons came to me. One of them was older than the other and I gave the Siwak to the younger. I was told that I should give it to the older and so I did."

Sahih al-Bukhari Book 4, Hadith 112