Abu Dawud
Fasting
Book Number: 007 / Hadith Number: 2431
Narated By One of the wives of the Prophet : Hunaydah ibn Khalid narrated from his wife on the authority of one of the wives of the Prophet (pbuh) who said: The Apostle of Allah (pbuh) used to fast the first nine days of Dhul-Hijjah, Ashura' and three days of every month, that is, the first Monday (of the month) and Thursday.