(81) باب صَوْمِ ثَلاَثَةِ أَيَّامٍ مِنَ الشَّهْرِ
It was narrated that Abu Hurairah said:
"The Messenger of Allah commanded me to sleep after praying Witr, to perform Ghusl on Friday and to fast three days of each month." (Sahih). (ID)
Reference (ID): Sunan an-Nasa'i 2407 (ID)
In-book reference (ID): Book 22, Hadith 318 (ID)
English translation (ID): Vol. 3, Book 22, Hadith 2409 (ID)