Praise be to Allah.
Muslim narrated in his Saheeh (1164) from Abu Ayyoob al-Ansaari (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever fasts Ramadaan then follows it with six days of Shawwaal, it is as if he fasted a lifetime.”
The apparent meaning of the hadeeth is that this reward can be attained only by the one who fasts six days in Shawwaal.
The scholars differed concerning one who fasts the six days at a time other than Shawwaal, whether that is due to an excuse or not. Does he attain the virtue of fasting them in Shawwaal or not? There are two views.
A number of Maalikis, and some Hanbalis are of the view that this virtue may be attained by the one who fasts six days in Shawwaal and afterwards, and that the hadeeth only mentioned Shawwaal in order to make things easier, because fasting them after Ramadaan is easier than doing it later on.
Al-‘Adawi said in his commentary on Sharh al-Khurashi (2/243): The Lawgiver only mentioned Shawwaal in order to make it easier with regard to fasting, not to restrict the ruling to that time only. No doubt doing it in the first ten days of Dhu’l-Hijjah along with what was narrated concerning the virtue of fasting at that time is better, because the purpose is achieved in addition to the extra reward for fasting on virtuous days. Doing it in Dhu’l-Qa’dah is also good. To sum up: The later you fast them, the greater the reward because it is more difficult. End quote.
It was narrated in Tahdheeb Furooq al-Quraafi by Muhammad ibn ‘Ali ibn Husayn, the mufti of the Maalikis in Makkah, and printed with al-Furooq (2/191), from Ibn al-‘Arabi al-Maaliki, that the words of the Prophet (peace and blessings of Allaah be upon him) “in Shawwaal” are mentioned by way of example, and that what is meant is that fasting Ramadaan counts as ten months, and fasting six days of Shawwaal counts as two months, and that is the view of the madhhab of Imam Maalik. If that is at a time other than Shawwaal then the ruling is the same. He said: This is very smart so learn it. End quote.
Ibn Muflih said in al-Furoo’ (3/108): It is possible that the reward may be attained even when fasting them at a time other than Shawwaal, according to some scholars. This was mentioned by al-Qurtubi, because the virtue of that is based on the fact that one good deed (hasanah) will be rewarded tenfold, as it says in the report of Thawbaan. And the recommendation of fasting in Shawwaal is because it is easier to fast as one is already used to fasting, and this is a kind of dispensation, and it is more appropriate to avail oneself of the dispensation.
It was also quoted by the author of al-Insaaf, who commented on it by saying: I say: This view is weak and is contrary to the hadeeth. Rather it is connected to the virtue of Ramadaan because it comes immediately after it and not because the good deed is rewarded tenfold, and because fasting them is equal to the obligatory fast of Ramadaan in virtue. End quote from al-Insaaf (3/344).
A number of the Shaafa’is were of the view that a person who does not fast six days in Shawwaal can make it up in Dhu’l-Qa’dah, but the reward will be less than that of the one who fasts them in Shawwaal. The person who fasts Ramadaan and follows it with six days of Shawwaal will have the reward of fasting a whole year of obligatory fasts, unlike the one who fasts Ramadaan and six days other than in Shawwaal. He will have the reward of Ramadaan and the reward of six naafil days.
Ibn Hajar al-Makki said in Tuhfat al-Muhtaaj (3/456): If a person fasts them along with Ramadaan every year, it will be like observing obligatory fasts for a lifetime, without multiplying the reward. If he fasts six other days, it will be like observing naafil fasts, without multiplying the reward. End quote.
He can only attain this virtue by fasting them in Shawwaal. This is the view of the Hanbalis.
It says in Kashshaaf al-Qinaa’ (2/338): The virtue of fasting them – i.e., the six days of Shawwaal – cannot be attained at any time other than Shawwaal, because of the apparent meaning of the reports. End quote.
But there is the hope that the person who fasted some of them and could not complete them because of an excuse will attain the reward and virtue thereof.
Shaykh Ibn Baaz (may Allaah have mercy on him) said: It is not prescribed to make them up after the end of Shawwaal, because they are Sunnah and the time for them has passed, whether one missed them for an excuse or otherwise.
He said concerning one who fasted four days in Shawwaal and did not complete six because of circumstances: Fasting the six days of Shawwaal is a mustahabb act of worship but is not obligatory; but you will have the reward of whatever you fast of them, and there is the hope of a complete reward if there was a legitimate shar’i excuse for not completing them, because the Prophet (peace and blessings of Allaah be upon him) said: “If a person falls sick or travels, Allaah will decree for him (the reward of) what he used to do when he was not travelling and was healthy.” Narrated by al-Bukhaari in his Saheeh. So you do not have to make up what you did not do. And Allaah is the Source of strength. End quote from Majmoo’ Fataawa al-Shaykh Ibn Baaz (15/389, 395).
To sum up:
Fasting six days at a time other than Shawwaal: some scholars regarded that as being like fasting them in Shawwaal, and some stated that there is virtue therein but it is less than the virtue of fasting six days in Shawwaal. And some scholars hope for the reward for the one who is not able to complete six days because of an excuse. The bounty of Allaah is great and His generosity knows no end. If this sister fasted two days in Dhu’l-Qa’dah to make up for what she missed of Shawwaal, that is good, and there is the hope that she will be rewarded in sha Allaah.
And Allaah knows best.