أَمَرَنِي رَسُولُ اللَّهِ صلى الله عليه وسلم بِثَلاَثٍ بِنَوْمٍ عَلَى وِتْرٍ وَالْغُسْلِ يَوْمَ الْجُمُعَةِ وَصَوْمِ ثَلاَثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ .
It was narrated that Abu Hurairah said: "The Messenger of Allah enjoyed three things upon me: To sleep after praying Witr, to perform Ghusal on Friday, and to fast three days of each month." (Sahih).