Abu Dharr al-Ghaffari · The Book of Fasting

"The Messenger of Allah said to me: 'O 'Abdullah bin 'Amr, you fast all the time and you do stand (in prayer) at night, but if you do that your eyes will become sunken and you will become exhausted. There is no fast for one who fasts every day of his life. Fasting a lifetime means fasting three days each month,

"My beloved Prophet advised me to do three things which I will never give up, if Allah wills. He advised me to pray Duha, to pray Witr before sleeping, and to fast three days of each month."

"The Messenger of Allah enjoyed three things upon me: To sleep after praying Witr, to perform Ghusal on Friday, and to fast three days of each month." (Sahih).

the Messenger of Allah used to fast nine days of Dhul-Hijjah, the day of 'Ashura', and three days of each month: The first Monday of the month, and two Thursday.

"The Prophet used to fast the ten (days), and three days of each month: Monday and Thursday."

"Fasting three days of each month is fasting for a lifetime, and the shining days of Al-Bid, the thirteenth, fourteenth and fifteenth."

"A Bedouin came to the Prophet with a rabbit that he had grilled it and placed it in front of him. The Messenger of Allah refrained from eating, but he told the people to eat. The Bedouin also refrained, and the Prophet said to him: 'What is keeping you from eating?' He said: 'I fast three days of the month.' He said: 'If you was to fast, fast the shining days."'