Prophet Muhammad ﷺ said:

"Whoever fasts Ramadan and then follows it with six days of (fasting in) Shawwal, it will be as if he had fasted for a year."

[Narrated by Muslim, Abu Dawud, At-Tirmidhi, An-Nisa& #39;i and Ibn Majah]

Popular Question by sisters:

Which should I do first? Qadha’ fasting to repay what I missed in Ramadan due to my period? Or prioritise 6 days of Shawwal?

1st Opinion: Perform the Qadha’ fasting first. And then follow up with the Sunnah fasting even if it is after Shawwal.

Reason: Because the Prophet PBUH said: “Whoever fasts Ramadan” i.e. the complete month - and then follows it with 6 days.

So if there were missed days, technically she has not fasted the whole of Ramadan yet to qualify for 6 days of Shawwal.

2nd Opinion: Prioritise Qadha’ fasting too. But it is not necessary to add on 6 days of sunnah fasting in Shawwal afterwards if all of the Qadha’ was done in Shawwal.

Reason: The Prophet’s words were generic: “and follows it with 6 days of fasting” regardless of the type of fast