´It was narrated from Jarir bin 'Abdullah that the Prophet said:` "Fasting three days of each month is fasting for a lifetime, and the shining days of Al-Bid, the thirteenth, fourteenth and fifteenth."
Explanation & Benefits
Hafiz Muhammad Ameen
In these three nights, the moon is full and remains visible throughout the night; therefore, they are called the "bright nights." The objective is to observe three fasts in the month. One may fast on these days, or according to Mondays and Thursdays, or as circumstances permit.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 2422