عَنْ أَبِي هُرَيْرَةَ رضى الله عنه عَنْ
رَسُولِ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «لَوْلَا أَنْ أَشُقَّ عَلَى أُمَّتِي لَأَمَرْتُهُمْ بِالسِّوَاكِ مَعَ كُلِّ وُضُوءٍ»
The Messenger of Allah (sallallahu alayhi wa sallam) said “Had I not feared burdening my Ummah, I would have commanded them to use Siwak with every ablution.” [Reported by Malik, Ahmad and An-Nasai. Ibn Khuzaima graded it Sahih (sound) and Al-Bukhari mentioned as a Muallaq (suspended – without its chain of narrators).
Bulugh al-Maram 37, Book 1, The Book of Purification, Hadith 37. 1 min read