The ruling on making up for the six Days after Shawwal

Question :

A woman fasts six days from the month of Shawwal every year. Then, during one of the years she was in the period of postnatal bleeding due to giving birth to her child at the beginning of the month of Ramadhan. She did not become pure until after Ramadhan was over. Then, after she became pure, she started making up for the missed days (of Ramadhan). Is she obligated also to make up for the six days (of Shawwal) after making up for the fast of Ramadhan, even if that is in a month other than Shawwal, or is she only required to make up for Ramadhan? Is fasting these six days from Shawwal always mandatory or not?

Answer:

Fasting six days of Shawwal is Sunnah (i.e., supereroga- tory) and it is not obligatory. This is due to the statement of the Prophet:
"Whoever fasts Ramadhan, and then follows it up with six (days of fasting) from Shawwal, then that is as if he fasted the entire time (i.e., year)."

This was recorded by Imam Muslim in his Sahih, and this mentioned Hadith proves that there is no harm in fasting them consecutively or separately due to the generality of its wording. To make haste in fasting them is better due to Allâh's Statement:
"And I hastened to You my Lord so that you would be pleased."

This is also due to what the Qur'anic Verses and the Prophetic Hadiths prove concerning the virtue of racing and making haste to the good. It is not obligatory to always perform this fast, but that is better. This is due to the Prophet's statement:
"The most beloved deed to Allah is that which its doer does consistently, even if it is small in amount."

It is not legislated to make up for this fast after the month of Shawwal is over, because it is Sunnah and its place has been missed, regardless of whether she abandoned it due to an excuse or without an excuse. And Allâh is the Giver of success.

Source:
Ash-Shaykh Ibn Baz
Fatawa Islamiyah, Vol. 3 Pages 336-337