It was narrated from Hunaidah bin Khalid, from his wife, from one of the wives of the Prophet , that the Messenger of Allah صلی اللہ علیہ وآلہ وسلم used to fast nine days of Dhul-Hijjah, the day of AshCira’, and three days of each month: The first Monday of the month, and two Thursdays. (Sahih).