Language:
كتاب الوضوء
4
Ablutions (Wudu')
(73)
Chapter: Siwak (to clean the teeth with Siwak which is a tooth-brush in the form of a pencil from the roots of the Arak tree
(73)
باب السِّوَاكِ
وَقَالَ ابْنُ عَبَّاسٍ بِتُّ عِنْدَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَاسْتَنَّ.

Narrated Abu Burda:

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."

حَدَّثَنَا أَبُو النُّعْمَانِ، قَالَ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ غَيْلاَنَ بْنِ جَرِيرٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِيهِ، قَالَ أَتَيْتُ النَّبِيَّ صلى الله عليه وسلم فَوَجَدْتُهُ يَسْتَنُّ بِسِوَاكٍ بِيَدِهِ يَقُولُ ‏ "‏ أُعْ أُعْ ‏"‏، وَالسِّوَاكُ فِي فِيهِ، كَأَنَّهُ يَتَهَوَّعُ‏.‏
Reference : Sahih al-Bukhari 244
In-book reference : Book 4, Hadith 111
USC-MSA web (English) reference : Vol. 1, Book 4, Hadith 245
  (deprecated numbering scheme)