Hudhayfah reported that whenever the Prophet ﷺ rose at night, he would clean his mouth thoroughly with the siwak.
كان النبي ﷺ إذا قام من الليل يشوص فاه بالسواك.
Bukhari narrated it in the Book of Wudu (245), and Muslim in the Book of Purification (255), both from the hadith of Jareer, from Mansur, from Abu Waail, from Huzaifa, and he mentioned the hadith.In the version narrated by Husayn bin Abdul-Rahman, from Abu Waail, in Muslim, it reads, "When he got up to perform tahajjud, he would rub his mouth with the tooth-stick." The word "shaws" means rubbing the teeth crosswise with the tooth-stick.