The Prophet ﷺ said, "Were it not that I would burden my community, I would have commanded them to use the siwak before every prayer."
حدثنا يحيى بن سعيد قال سمعناه من الأعمش حدثني عبد الله بن يسار عن عبد الرحمن بن أبي ليلى
عن النبي ﷺ قال لولا أشق على أمتي لأمرتهم بالسواك مع كل صلاة
Its isnad is sahih, it has occurred many times before. See and its cross-references. See also
and its cross-references.