Language:
كتاب الأطعمة
70  
Food, Meals
(51)
Chapter: To rinse the mouth after taking meals
(51)
باب الْمَضْمَضَةِ بَعْدَ الطَّعَامِ
Sahih al-Bukhari 5454
Narrated Suwaid bin An Nu`man:

We went out with Allah's Messenger (ﷺ) to Khaibar, and when we reached As-Sahba', the Prophet (ﷺ) asked for food, and he was offered nothing but Sawiq. We ate, and then Allah's Messenger (ﷺ) stood up for the prayer. He rinsed his mouth with water, and we too, rinsed our mouths.

حَدَّثَنَا عَلِيٌّ، حَدَّثَنَا سُفْيَانُ، سَمِعْتُ يَحْيَى بْنَ سَعِيدٍ، عَنْ بُشَيْرِ بْنِ يَسَارٍ، عَنْ سُوَيْدِ بْنِ النُّعْمَانِ، قَالَ خَرَجْنَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم إِلَى خَيْبَرَ، فَلَمَّا كُنَّا بِالصَّهْبَاءِ دَعَا بِطَعَامٍ فَمَا أُتِيَ إِلاَّ بِسَوِيقٍ، فَأَكَلْنَا فَقَامَ إِلَى الصَّلاَةِ، فَتَمَضْمَضَ وَمَضْمَضْنَا‏.‏
Reference : Sahih al-Bukhari 5454
In-book reference : Book 70, Hadith 83
USC-MSA web (English) reference : Vol. 1, Book 65, Hadith 365
  (deprecated numbering scheme)