The Excellence of the Voluntary Fast

The Messenger of Allah encouraged the fasting of the following days: 

1) Fasting the six days of Shawwaal, as the Prophet (sal-Allahu 'alyhe wa sallam) said:

((Whoever fasts Ramadan and then follows it up with (any) six (days of fasting) in Shawwaal, then it would be as if he has fasted the (whole) year)),

[Transmitted by Muslim and others]

The scholars have noted that each good deed is rewarded by ten (10), and therefore fasting the month of Ramadan is equivalent to fasting ten (10) months, and the six (6) days being equivalent to two (2) months; So the total sum is equivalent to twelve (12) months (i.e. a year);

2) Fasting the ninth day of Dhul-Hijjah, the day of 'Arafah - for those not performing the Hajj.

The Messenger of Allah (sal-Allahu 'alayhe wa sallam) said:

((The fast on the day of 'Arafah is an expiation for (the sins of) two years: the previous (year) and the following (year), and the fast of the day of 'Aashooraa is an expiation for (the sins of) the previous year)),

[Transmitted by Muslim and others] 

Once, the Messenger of Allah was brought some laban and he drank it whilst he was addressing the people in 'Arafah, and he (sal-Allahu 'alayhe wa sallam) said:

((There are no days in which righteous actions are more beloved to Allah than these days (i.e. the ten (10) days of Dhul-Hijjah)). It was said: O Messenger of Allah, not even jihaad in the path of Allah? He said:

((Not even jihaad in the path of Allah, except for a man who leaves (for jihaad) with his wealth and does not return with anything of it)),

[Transmitted by al-Bukhaaree] 

3) The fast of the Day of 'Aashooraa., including the day before or the day after.

The Messenger of Allah (sal-Allahu 'alayhe wa sallam) said:

((Indeed this is the Day of 'Aashooraa., and it has not been presecribed (obligated) upon you to fast it. However, I am fasting, and whoever wishes to fast may do so and whoever wishes to refrain from doing so, may do so)),

[The authenticity of this narration has been agreed upon by al-Bukhaaree and Muslim]

And the Messenger of Allah (sal-Allahu 'alayhe wa sallam) also said:

((And if I remain until the following year, then indeed I will fast the ninth (of Muharram along with the 10th (day of 'Aashooraa.))),

[Transmitted by Muslim] 

4) Fasting most of Sha'baan.

((The Messenger of Allah used to fast most of Sha'baan)),

[The authenticity of this narration has been agreed upon by al-Bukhaaree and Muslim] 

5) The fast of (every) Monday and Thursday.

The Messenger of Allah (sal-Allahu 'alayhe wa sallam) said:

((The actions (of the son of Aadam) are presented (before Allah) (every) Monday and Thursday, and I like it that my actions are presented whilst I am fasting)),

[Saheeh, narrated by an-Nasaa.ee. Refer to Saheeh al-Jaami' No.2956] 

And he (sal-Allahu 'alayhe wa sallam) was asked about fasting (every) Monday, and he said:

((That is the day on which I was born, and (the day) on which revelation descended upon me)),

[Transmitted by Muslim] 

6) Fasting the days of al-Biyadh, as one of the Sahaabah (radhi-yAllahu 'anhu) said:

((The Messenger of Allah (sal-Allahu 'alayhe wa sallam) encouraged us to fast (every) month the three days of the full moon, the thirteenth, the fourteenth and the fifteenth)),

[Transmitted by an-Nasaa.ee and others and its grade of authenticity is that of Hasan. Refer to Silsilah as-Saheehah, page 93] 

7) The fast of Prophet Daawood ('alayhis-salaam), i.e. fasting every other day.

The Messenger of Allah (sal-Allahu 'alayhe wa sallam) said:

((The most beloved fast to Allah is the fast of Daawood, and the most beloved prayer to Allah is the prayer of Daawood. He used to sleep half the night and stand for prayer for a third of the night and used to sleep a sixth of the night, and he used to fast every other day)),

[The authenticity of this narration has been agreed upon by al-Bukhaaree and Muslim]