Whenever the Messenger of Allah ﷺ rose at night to perform the tahajjud prayer, he would clean his mouth thoroughly with the siwak.
حدثنا محمد بن عبد الله بن نمير حدثنا أبو معاوية وأبي عن الأعمش ح و حدثنا علي بن محمد حدثنا وكيع عن سفيان عن منصور وحصين عن أبي وائل
كان رسول الله ﷺ إذا قام من الليل يتهجد يشوص فاه بالسواك
Bukhari narrated it in the Book of Friday Prayer, chapter "Using the Tooth-Stick on Friday," no. 889, and Muslim narrated it in the Book of Purification, chapter "The Virtue of Perfecting Wudu Despite Hardship," no. 255, from the hadith of Sufyan, through this route. It has other paths of transmission in both of their collections. Muslim also narrated it from Ibn Numayr, through this route.