Sunan an Nasai
534
Sahih+2

It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:"Were it not that I would impose too much difficulty on my Ummah, I would have commanded them to delay 'Isha' and to use the Siwak for every prayer

SahihAbu Ghuddah
DaifAl-Albani