Messenger of Allah ﷺ said, "If I had not found it hard for my followers or the people, I would have ordered them to clean their teeth with Siwak for every prayer."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لَوْلاَ أَنْ أَشُقَّ عَلَى أُمَّتِي أَوْ عَلَى النَّاسِ لأَمَرْتُهُمْ بِالسِّوَاكِ مَعَ كُلِّ صَلاَةٍ  

Messenger of Allah ﷺ said, "I have told you repeatedly to use the Siwak. (The Prophet ﷺ put emphasis on the use of the Siwak.)  

قَالَ رَسُولُ اللَّهِ ﷺ أَكْثَرْتُ عَلَيْكُمْ فِي السِّوَاكِ  

When the Prophet ﷺ got up at night (for the night prayer), he used to clean his mouth .  

كَانَ النَّبِيُّ ﷺ إِذَا قَامَ مِنَ اللَّيْلِ يَشُوصُ فَاهُ