"Fasting three days of each month is fasting for a lifetime, and the shining days of Al-Bid, the thirteenth, fourteenth and fifteenth."
Sunan an-Nasa'i Book 22, Hadith 331
← Previous Hadith "The Messenger of Allah used to enjoin fasting three days: The first Thursday, and Monday and Monday."

Sunan an-Nasa'i Book 22, Hadith 330 Next Hadith → "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."'

Sunan an-Nasa'i Book 22, Hadith 332