The Prophet ﷺ said: ʿWere it not that it would be too difficult for the ummah, I would have commanded them to use the siwak at the time of every prayer.” (Using translation from Aḥmad 607)
("استَاكُوا -لولا أنْ أنْ أشُقَّ على أُمَّتِي لأمرْتُهم بالسواك عند كل صلاة".