If a person is observing an optional fast and something happens and he has to break his fast, then he should break his fast. You do not have to make up the day when you broke your fast, because the one who is observing an optional fast is in charge of himself.

If you have an excuse that keeps you from fasting the six days of Shawwal in Shawwal because you have to make up missed fasts, then you may fast six days of Shawwal in Dhul-Qa'dah

`Eid Al-Fitr is just one day on which it is prohibited to fast. As for the second and third days of Shawwal, it is not prohibited to fast on those days. It is permissible to fast it to make up a missed Ramadan fast or as a voluntary fast.

Some scholars view that so long as there is sufficient time to make up missed fasts, it is permissible to observe optional fasts.

Fasting in Sha’ban in the second half is not allowed and that is either makruh or haram, except for the one who has the habit of fasting regularly or who is continuing after fasting during the first half of Sha’ban. For more, see the detailed answer.

It is recommended to fast a great deal in the month of Sha’ban. The Prophet Muhammad (peace and blessings be upon him) used to fast the whole of Sha’ban. For more, please see the detailed answer.

There is no sound hadith to indicate that there is any special virtue in fasting in Rajab. But there is a report from the Prophet (peace and blessings be upon him) which indicates that it is recommended to fast during the sacred months. For more, please see the detailed answer.