"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).
أَمَرَنِي رَسُولُ اللَّهِ ﷺ بِنَوْمٍ عَلَى وِتْرٍ وَالْغُسْلِ يَوْمَ الْجُمُعَةِ وَصِيَامِ ثَلاَثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ