(9) باب طُولِ الْقِيَامِ فِي صَلاَةِ اللَّيْلِ
Narrated Hudhaifa:
Whenever the Prophet (ﷺ) got up for Tahajjud prayer he used to clean his mouth (and teeth) with Siwak.
Reference: Sahih al-Bukhari 1136
In-book reference: Book 19, Hadith 17
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 21, Hadith 237