The importance of fasting on Mondays and Thursdays.

 The importance of fasting on Mondays and Thursdays. 

Alhamdulillaah, fasting on Mondays and Thursdays are sunnah of the messenger of Allah salla Allahu alayhi wasalam. 

As reported in hadith, 

It was narrated from Jubair bin Nufair that a man asked Aishah about fasting and she said:

The Messenger of Allah used to fast all of Shaban, and he made sure to fast on Mondays and Thursdays." '" '

Sunan an-Nasa'i 2186.

It was narrated from Abu Hurairah that the Prophet (ﷺ) used to fast on Mondays and Thursdays. It was said:

“O Messenger of Allah, why do you fast on Mondays and Thursdays?” He said: “On Mondays and Thursdays Allah forgivesevery Muslim except two who have forsaken one another. He says: ‘Leave these two until they reconcile.’”

Sunan Ibn Majah. 

Vol. 1, Book 7, Hadith 1740.

So Mondays are days our deeds are written afresh and thursdays are days our deeds are taken to Allah so the messenger of Allah salla Allahu alayhi wasalam used to fast on mondays and thursdays. 

We have ayyamid bid(the white days).

The white days are the three days fasting which one does and fasting three days of every month is sunnah and like one has fasted whole year. 

As reported in hadith, 

Mu'adha al-'Adawiyya reported that she asked 'A'isha, the wife of the Messenger of Allah (ﷺ), whether theMessenger of Allah (ﷺ) observed fasts for three days during every month. She said:

Yes I said to her: Which were (the particular) days of the month on which he observed fast? She said He was not particular about the days of the month on which to observe fast.

Sahih Muslim 1160.

It is not necessarily that one fasts on 13th, 14th and 15th day.

One can fast on any day of the month but should be three days fasting.