Abdul Malik bin 'Umayr al-Qabti عبد الملك بن عمير بن سويد القبطي · The Book of Fasting

"There are four things which the Prophet never gave up: Fasting 'Ashura', (fasting during) the ten days, (fasting) three days of each month, and praying two Rak'ahs before Al-Ghadah (Fajr)."