Volume 3, Book 31, Number 202:
Narrated Abu Huraira (radiallaahu `anhu):
My friend (the Prophet (sallallaahu `alayhi wasallam)) advised me to observe three things:
(1) to fast three days a month;
(2) to pray two Rakat of Duha prayer (fore-noon prayer); and
(3) to pray Witr before sleeping.
it is mustahabb to fast three days each month, and it is best to fast the ayaam al-beed, which are the 13th, 14th and 15th of the month.
It was narrated that ‘Abd-Allaah ibn ‘Amr ibn al-‘Aas (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said to me:
“It is sufficient for you to fast three days every month, because for every good deed you will have (the reward of) ten like it, so that will be like fasting for a lifetime.”
Narrated by al-Bukhaari (1874); Muslim (1159).
Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allaah have mercy on him) was asked:
It was narrated in the hadeeth that the Prophet (peace and blessings of Allaah be upon him) advised Abu Hurayrah (may Allaah be pleased with him) to fast three days of each month. When should these fasts be observed, and should they be one after the other?
It is permissible to fast these days one after the other or separately, and they may be at the beginning of the month, or in the middle, or at the end. The matter is broad in scope, praise be to Allaah, because the Messenger of Allaah (peace and blessings of Allaah be upon him) did not state any specific days. ‘Aa’ishah (may Allaah be pleased with her) was asked: Did the Messenger of Allaah (peace and blessings of Allaah be upon him) fast three days of each month? She said: Yes. It was asked: In which part of the month did he fast? She said: He would not bother in which part of the month he would fast. Narrated by Muslim, (1160). But the 13th, 14th and 15th are better, because these are al-ayyaam al-beed.
Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen, 10/ question no. 376.
Is it necessary to make an intention before fasting? If yes, when to make that intention?
Narrated Salama bin Al-Akwa (radiallaahu `anhu):
Once the Prophet (sallallaahu `alayhi wasallam) ordered a person on ‘Ashura’ (the tenth of Muharram) to announce, “Whoever has eaten, should not eat any more, but fast, and who has not eaten should not eat, but complete his fast (till the end of the day).
It was narrated by Ibn ‘Umar from Hafsah (may Allaah be pleased with her) that the Prophet (peace and blessings of Allaah be upon him) said:
Whoever does not have the intention of fasting before Fajr, there is no fast for him.
Narrated by Imam Ahmad, the authors of al-Sunan, Ibn Khuzaymah and Ibn Hibbaan; they classed it as saheeh and marfoo’.
Obligatory or Voluntary?
Summary: For obligatory fasts, intention has to be made before Fajr that day. But for voluntary fasts, intention can be made later on during the day if one hasn’t eaten/drunk/had intercourse after Fajr that day. Read below for details.
It is essential to make the intention to fast the month of Ramadan at night, before Fajr. It is not sufficient to start fasting it that day without the intention. Whoever finds out at the time of Duha that today it is Ramadan and makes the intention of fasting has to refrain from eating until sunset, and he also has to make up that day. This is with regard to obligatory fasts. With regard to naafil (voluntary) fasts it is permissible to make the intention to fast on the day, if you have not eaten or drunk or had intercourse after Fajr, because it was proven in the hadeeth of ‘Aa’ishah (may Allaah be pleased with her) that the Prophet (peace and blessings of Allaah be upon him) entered upon her one day at duha time and said, “Do you have anything (any food)?” She said, “No.” He said, “Then I am fasting.” Narrated by Muslim in his Saheeh.