The Messenger of Allah ﷺ, whenever he rose at night, would clean his mouth thoroughly with the siwak.
حدثنا محمد بن كثير حدثنا سفيان عن منصور وحصين عن أبي وائل
أن رسول الله ﷺ كان إذا قام من الليل يشوص فاه بالسواك
Reference (takhrij): Bukhari narrated it in the Book of Wudu, Chapter on the Miswak, no. 245, 889, and Muslim in the Book of Purification, Chapter on the Miswak, no. 255, from the hadith of Sufyan Thawri through this same chain. Nasai also narrated it, no. 2, as did Ibn Majah.