"The Messenger of Allah commanded me to pray two Rakahs of Duha, and not to sleep until I had prayed witr, and to fast three days each month."
Sunan an-Nasa'i Book 22, Hadith 280
← Previous Hadith "The Messenger of Allah used to fast three days in the middle of every month, and he rarely did not fast on Friday."

Sunan an-Nasa'i Book 22, Hadith 279 Next Hadith → he heard Ibn 'Abbas, when he was asked about the fast of 'Ashura' say: "I do not know that the Prophet fasted any day because of its virtue, except this day" meaning the month of Ramadan and the day of Ashura.'

Sunan an-Nasa'i Book 22, Hadith 281