Assalamu Alaikum What are the Sunnah in observing Nafil fasting? During which days is it necessary to observe fasting in a week? During which days is it necessary to observe fasting in a month? Apart form these, in which days and which months is it Sunnat to observe fasting?
There are no days specified specially for Nafl Fastings. It can be observed all the days excluding the month of Ramadhan, two festival days and the days of Thashreeq (11th 12th and 13th of Zul Haj).
However there are some days, virtues of which are mentioned in Ahadees. They are; first 9 days of Zul Haj, Day of Aashoora the 10th of Muharram (to add 9th or 11th with it), and 6 days in Shawwal. Apart from this, it is Nafl and Musthahab to observe fasting on Ayyamul Beedh (13th, 14th and 15th of every month). Rules of nullifying and acceptance of Nafl Fastings are same as of the Fardh Fastings. However, it is not correct for a woman to keep Fasting without the permission of her husband while he is present. By breaking a Nafl Fasting after being observed, Qadha of same would become incumbent.
کما فی اعلاء السنن:وعن ابي أيوب الانصاري،عن رسول الله صلى الله عليه وسلم قال من صام رمضان ثم اتبعه ستا من شوال فذاك صيام الدهراھ(/9/8/153)۔
وفي اعلاء السنن :أن أحاديث المتن بظاهرها تدل على وجوب القضا وهذه على عدم وجوبه فيرجع الأول بعموم قاعدة اذا تعارض الحلال والحرام غلب الحرام اھ(9/8/141) ۔
وفي خلاصة الفتاوى:المرأة لا تصوم التطوع الا بإذن زوجها إن أمكنه وطيها وله أن يفطرها اھ(1/266) ۔
وفي الدر المختار:( ونفل كغيرهما ) يعد السنة كصوم عاشورا مع التاسع والمندوب كأيام البيض من كل شهراھ(2/374) ۔