Hudhayfah reported that whenever the Prophet ﷺ rose at night, he would clean his mouth thoroughly with the siwak.
حدثنا سفيان بن عيينة عن منصور عن أبي وائل
أن النبي ﷺ كان إذا قام من الليل يشوص فاه بالسواك
Its isnad is sahih, and its narrators are well-known trustworthy men. The hadith was reported by Bukhari 1/356 no. 245 in Fath al-Bari, in the book of wudu, Muslim 1/220 no. 255, Abu Dawud 1/15 no. 55, Nasai 1/8 no. 2, and Ibn Khuzayma 1/70, all in the book of purification, and Humaydi 1/210 no. 441.