Abu Ayyub al-Ansari, may Allah be pleased with him, reported that the Messenger of Allah, peace and blessings be upon him, said:

The report promises a reward like continual fasting to someone who fasts Ramadan and then follows it with six days of Shawwal. Muslim, 1164. Fasting these days is recommended for both men and women, and the stated virtue is connected to that sequence.

Thawban, may Allah be pleased with him, also reported:

This describes the six days after the end of Ramadan as completing the year. Ibn Majah, 1715, excerpt; authenticated by al-Albani. Scholars explain the tenfold reward: Ramadan corresponds to ten months, and six days to two months, making the reward like fasting a year. This does not replace any obligatory fast or authorise fasting every day of the year, including days on which fasting is forbidden.

You may begin on the second day of Shawwal, after Eid al-Fitr, and continue until the month ends. Fasting on Eid itself is forbidden, and that day cannot count among the six. The Prophet's prohibition of fasting on Eid al-Fitr is recorded in al-Bukhari, 1990.

You may fast the days consecutively or separately, early, midway through or late in the month. Ibn Baz ruled accordingly and recommended beginning promptly before interruptions arise. The fasts are not restricted to Shawwal 2–7. You may leave days between them or choose dates that fit your work and family circumstances, provided you complete the six within Shawwal after your outstanding Ramadan fasts, under the ruling explained next.

Begin with any outstanding Ramadan fasts, then fast the six if possible. This is Ibn Baz's ruling. He explained that the obligation takes priority and that the hadith describes fasting Ramadan and then following it with six days. Someone who still owes Ramadan days has not yet completed Ramadan's fast.

Some jurists permit voluntary fasting before qada when there is still ample time to make up the obligation. Completing qada first, then fasting six separate days, observes the sequence in the report and gives priority to what you owe over voluntary worship.

For example, if you owe three days, fast those with the intention of qada, then another six with the intention of the Shawwal fasts: nine days in total. You do not need to leave non-fasting days between the two, but you may if that suits your capacity. See Making Up Missed Ramadan Fasts, Fidyah and Kaffarah for the duties arising from missed fasts.

Do not rely on one day as both a makeup day and a complete, separate day of the six. Ibn Baz ruled that the six need their own intention and days, and that combining their intention with qada does not appear to secure their reward. Intend the obligatory fasts for their days and give the six their own days.

Some Shafii jurists, including al-Ramli, discussed receiving the basic reward of voluntary fasting when qada takes place in Shawwal, while distinguishing this from the full reward attached to following Ramadan with six days. The issue is disputed; giving the six their own days after qada avoids relying on that disputed combination.

Under the ruling above, give priority to qada even if too little time remains for the six. If illness or postpartum bleeding, followed by the necessary makeup fasts, leaves no time for the six, you have not sinned by missing them. Do not attempt what you cannot manage.

Scholars differ about fasting them after Shawwal because of a valid excuse. Ibn Baz ruled that their time has passed and that they are not made up afterwards, even when missed for an excuse. Ibn Uthaymin permitted someone prevented by an excuse, such as qada occupying the month, to fast them afterwards, unlike someone who delayed without an excuse. Six days in Dhul-Qadah should therefore not be treated as a general substitute for Shawwal. Someone with a continuing excuse should seek qualified advice about the actual circumstances.

Neither position makes it obligatory to make up these missed voluntary fasts. Nor does this discussion mean that a permissible voluntary fast after Shawwal has no reward: the question is whether it receives the specific virtue of Shawwal's six days.

The cautious approach for receiving a full day's reward is to intend each fast during the night before Fajr. Intention means resolving in your heart to fast; there is no special spoken formula for these six days. Obligatory Ramadan makeup fasts require their qada intention before dawn.

Observe the usual fasting rules, abstaining from invalidators from true dawn until sunset, maintaining the prayers and avoiding lying and backbiting. For the basic rules, see Fasting for Beginners.

Plan days you can manage instead of leaving all six until a busy end of the month. If menstruation or illness interrupts your plans, follow its relevant rulings and continue when the impediment ends and time remains. The days do not need to run consecutively.