1262 – Abu Dharr (may Allah be pleased with him) narrated that the Messenger of Allah ﷺ said, “When you fast three days of the month, fast the thirteenth, fourteenth, and fifteenth.” Recorded by al-Tirmidhi, who graded it hasan.

1263 – Qatadah ibn Milhan (may Allah be pleased with him) said, “The Messenger of Allah ﷺ used to command us to fast on the White Days: the thirteenth, fourteenth, and fifteenth.” Recorded by Abu Dawud.

1264 – Ibn Abbas (may Allah be pleased with them both) said, “The Messenger of Allah ﷺ would never forgo fasting on the White Days, whether he was resident or traveling.” Recorded by al-Nasa’i with a hasan chain of transmission.

[Explanation]
Imam al-Nawawi, may Allah have mercy on him, placed these two chapters in Riyad al-Salihin to clarify the merit of fasting on Monday and Thursday and of fasting three days in every month.

With regard to fasting on Monday, the Prophet ﷺ was asked about it and said, “That is the day on which I was born, on which I was sent—or on which revelation first came down to me—and it is also the day on which I died.” Thus the Prophet ﷺ was born on a Monday, but the precise month is not definitively established: was it Rabi‘ al-Awwal or another month, and was it the twelfth of that month or a different day? Only