Sahih al-Bukhari 244
Sahih al-Bukhari · Book 4: Ablutions (Wudu') · 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
Narrated Abu Burda:
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.
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."