كتاب الطهارة
1  
The Book of Purification
(7)
Chapter: Permitting The Usage Of Siwak In The Afternoon For One Who Is Fasting
(7)
باب الرُّخْصَةِ فِي السِّوَاكِ بِالْعَشِيِّ لِلصَّائِمِ ‏‏
Sunan an-Nasa'i 7
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."
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، عَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ لَوْلاَ أَنْ أَشُقَّ عَلَى أُمَّتِي لأَمَرْتُهُمْ بِالسِّوَاكِ عِنْدَ كُلِّ صَلاَةٍ ‏"‏ ‏.‏
Grade: Sahih (Darussalam)
Reference : Sunan an-Nasa'i 7
In-book reference : Book 1, Hadith 7
English translation : Vol. 1, Book 1, Hadith 7