When the Prophet (p.b.u.h) got up at night (for the night prayer), he used to clean his mouth .
Sahih al-Bukhari Book 11, Hadith 14
← Previous Hadith Allah's Messenger (ﷺ) said, "I have told you repeatedly to use the Siwak. (The Prophet (ﷺ) put emphasis on the use of the Siwak.)

Sahih al-Bukhari Book 11, Hadith 13 Next Hadith → `Abdur-Rahman bin Abi Bakr came holding a Siwak with which he was cleaning his teeth. Allah's Apostle looked at him. I requested `Abdur-Rahman to give the Siwak to me and after he gave it to me I divided it, chewed it and gave it to Allah's Messenger (ﷺ). Then he cleaned his teeth with it and (at that time) he was resting against my chest.

Sahih al-Bukhari Book 11, Hadith 15