(54) باب مَا جَاءَ فِي صَوْمِ ثَلاَثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ
Abu Hurairah narrated:
"The Messenger of Allah took a covenant from me for three: To not sleep except after performing Witr, to fast three days of every month, and to perform the Duha prayer."
Reference: Jami` at-Tirmidhi 760
In-book reference: Book 8, Hadith 79
English translation: Vol. 2, Book 3, Hadith 760