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)  

قَالَ رَسُولُ اللهِ ﷺ «لَوْلَا أَنْ أَشُقَّ عَلَى أُمَّتِي لَأَمَرْتُهُمْ بِالسِّوَاكِ عِنْدَ كُلِّ صَلَاةٍ»