What is the virtue of performing fasting on the 13th, 14th and 15th days of lunar months (Ayyam al-Bid)?

Dear Brother / Sister,

There are many hadiths related to the virtue of performing nafilah fasting on the 13th, 14th and 15th days of lunar months, that is, on the brightest days of the moon called Ayyam al-Bid.

As a matter of fact, Hz. Hafsa states the following:

"I can say that the Messenger of Allah (pbuh) hardly ever abandoned four things: Fasting on the day of Ashura, fasting on the first ten days of Dhul-Hijjah, fasting on the 13^th, 14^th and 15^th days of every month and performing two rak’ahs before the fard of the morning prayer." (Ahmad bin Hanbal, Nasai)

The days mentioned in the hadiths are the 13th, 14th and 15th days of lunar months based on Hijri Calendar. The prayer performed in the morning is the sunnah of the morning prayer. 

The Prophet performed fasting on “Ayyam al-Bid” before fasting in Ramadan was rendered fard (Ahmad, 5/246; Tirmidhi, Sawm, 41, 54); he continued this fasting after fasting in Ramadan was rendered fard (Tirmidhi, Sawm, 54). He encouraged this fasting with the following hadiths: "If a person performs fasting three days every month, he is regarded to have fasted during his whole life." (Tirmidhi, Sawm, 54, III, 135) “When you want to perform fasting (outside Ramadan) fast on the 13^th, 14^th and 15^th days of the month.” (Suyuti, al-Jamius-Saghir, 1/66 H. No: 892)

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