Repayment & Voluntary Fasting

1. Whoever misses any days in Ramadhan must repay them from other days.
2. Sunnah is to do this immediately (some opinions required consecutively.
3. If it comes to the next Shaaban and there are only enough days left to pay what is due, then consecutive fasting is wajib.
4. One who owes days of Ramadhan cannot fast any other voluntary fast until they are paid.
5. It is sunnah to fast voluntary fasts on other days.  The best of all is saum dawood which is fasting every other day.  Fasting all days (intending forever) is forbidden.
6. It is sunnah to fast the "White Days" which are the 13th, 14th and 15th of the month (lunar, of course).
7. Also, to fast Thursday and Monday.
8. And six days of Shawwal.
9. Also, the month of Muharram. The strongest of that is 'aashooraa (the 10th) - which must be preceded or followed by another day of fasting - and it is an expiation for the year.
10. And ten days of dhil-hijja. The strongest of that is the day of Arafat and it is an expiation of two years.
11. It is makrooh (disliked) to intend Rajab with fasting because this is a month which was honored in the jahiliya.
12. Likewise to intend Friday with fasting unless accompanied by Thursday or Saturday (strong: Muslim & Bukhari).  (The same is said about Saturday, but there is doubt about the narrations involved.)
13. Likewise (makrooh), fasting the "day of doubt", i.e., the 30th of Shaaban when the moon was not sighted.
14. It is haraam to fast either of the two 'Eids.
15. When one begins a voluntary fast, completing it is not wajib, but completing obligatory fasting is wajib (except with legitimate reason).