Sunan an Nasai
7
Sahih+2

It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:"Were it not that it would be too difficult for my Ummah, I would have commanded them to use the Siwak at (the time of) every Salah

SahihAbu Ghuddah
SahihAl-Albani