What are the days for which fasting is considered a confirmed Sunnah, and what is the ruling on fasting the Hijri New Year, mid-Sha'ban, and the like?

Fasting is only obligatory during the month of Ramadan or for other reasons such as making up missed fasts (qada'), vows (nadhr), and expiations (kaffarat). Voluntary fasting is recommended, such as on the Day of Arafah, Ashura, Mondays and Thursdays, the Ayyam al-Bid (the White Days), and six days of Shawwal, with some being more emphasized than others. The most emphasized among them is fasting on the Day of Arafah for those who are not performing Hajj, then the Day of Ashura, then six days of Shawwal. Fasting on the Day of Arafah expiates sins for two years, fasting on Ashura expiates sins for one year, and fasting six days of Shawwal after Ramadan is like fasting for an entire year. As for fasting on the Hijri New Year or singling out a day in Rajab for fasting, these are innovations (bid'ah), as there is no authentic text supporting them.