In the name of Allah, the Gracious, the Merciful
It is highly recommended to fast six days of the month of Shawwal after completing the fast of Ramadan.
Abu Ayub reported: The Messenger of Allah, peace and blessings be upon him, said:
مَنْ صَامَ رَمَضَانَ ثُمَّ أَتْبَعَهُ سِتًّا مِنْ شَوَّالٍ كَانَ كَصِيَامِ الدَّهْرِ
Whoever fasts the month of Ramadan and then follows it with six days of fasting during the month of Shawwal will be as if he has fasted for the year.
Source: Ṣaḥīḥ Muslim 1164, Grade: Sahih
The reason it will be as if he or she has fasted the whole year is because Allah multiplies sincere good deeds by ten or more.
Ibn Abbas reported: The Messenger of Allah, peace and blessings be upon him, said:
فَمَنْ هَمَّ بِحَسَنَةٍ فَلَمْ يَعْمَلْهَا كَتَبَهَا اللَّهُ عِنْدَهُ حَسَنَةً كَامِلَةً وَإِنْ هَمَّ بِهَا فَعَمِلَهَا كَتَبَهَا اللَّهُ عَزَّ وَجَلَّ عِنْدَهُ عَشْرَ حَسَنَاتٍ إِلَى سَبْعِ مِائَةِ ضِعْفٍ إِلَى أَضْعَافٍ كَثِيرَةٍ
Whoever intends to perform a good deed but does not do it, then Allah will record it as a complete good deed. If he intends to do it and does so, then Allah the Exalted will record it as ten good deeds up to seven hundred times as much or even more.
Source: Ṣaḥīḥ al-Bukhārī 6126, Grade: Muttafaqun Alayhi
Hence, thirty days of Ramadan and six days of Shawwal will equal three hundred and sixty days of fasting or about one year. This understanding is confirmed by another reliable narration.
Thawban reported: The Messenger of Allah, peace and blessings be upon him, said:
صِيَامُ رَمَضَانَ بِعَشَرَةِ أَشْهُرٍ وَصِيَامُ السِّتَّةِ أَيَّامٍ بِشَهْرَيْنِ فَذَلِكَ صِيَامُ السَّنَةِ
Fasting the month of Ramadan is like ten months of fasting and fasting six days of Shawwal is like two months of fasting, so those together is like fasting a year.
Source: Ṣaḥīḥ Ibn Khuzaymah 2115, Grade: Sahih
Therefore, we should take advantage of this opportunity to gain a tremendous amount of rewards for a comparatively small amount of effort.
One of the purposes of fasting during the month of Shawwal is to continue the habit of fasting that we have developed during Ramadan. If we do not fast any days of Shawwal, it will be much more difficult to make fasting a regular habit throughout the year.
We should use the good habits we developed during Ramadan to begin practicing the voluntary (sunan) days of fasting, such as fasting on the days of Arafat and Ashura, fasting Mondays and Thursdays, and fasting three days in the middle of every month.
Abu Qatadah reported: A man came to the Messenger of Allah, peace and blessings be upon him, and he said, “What is your view about fasting on the day of Arafat?” The Prophet said:
يُكَفِّرُ السَّنَةَ الْمَاضِيَةَ وَالْبَاقِيَةَ
It will expiate the sins of the previous and upcoming years.
The man said, “O Messenger of Allah, what is your view about fasting the day of Ashura?” The Prophet said:
يُكَفِّرُ السَّنَةَ الْمَاضِيَةَ
It will expiate the sins of the year.
Source: Ṣaḥīḥ Muslim 1162, Grade: Sahih
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
تُعْرَضُ الْأَعْمَالُ يَوْمَ الِاثْنَيْنِ وَالْخَمِيسِ فَأُحِبُّ أَنْ يُعْرَضَ عَمَلِي وَأَنَا صَائِمٌ
The deeds are presented on Monday and Thursday. Thus, I love for my deeds to be presented while I am fasting.
Source: Sunan al-Tirmidhī 747, Grade: Sahih
Abu Dharr reported: The Messenger of Allah, peace and blessings be upon him, said:
إِذَا صُمْتَ مِنْ الشَّهْرِ ثَلَاثَةَ أَيَّامٍ فَصُمْ ثَلَاثَ عَشْرَةَ وَأَرْبَعَ عَشْرَةَ وَخَمْسَ عَشْرَةَ
If you are going to fast three days of the month, then fast on the thirteenth, fourteenth, and fifteenth days.
Source: Sunan al-Tirmidhī 761, Grade: Sahih
Even if one is incapable or finds it too difficult to fast six days of Shawwal, then he should fast at least a few days or as much as he can in order to make fasting a regular habit in each month. The consistency of a good practice is more important than its perceived size, as Allah loves good deeds that are done regularly even if they are small.
Aisha reported: The Messenger of Allah, peace and blessings be upon him, said:
وَاعْلَمُوا أَنَّ أَحَبَّ الْعَمَلِ إِلَى اللَّهِ أَدْوَمُهُ وَإِنْ قَلَّ
Know that the most beloved deed to Allah is that which is done regularly even if it is small.
Source: Ṣaḥīḥ al-Bukhārī 6099, Grade: Sahih
Therefore, let us reinforce the good habits we have cultivated during Ramadan and make fasting for some days a regular habit in every month, even if only a few days.
Success comes from Allah, and Allah knows best.