Voluntary fasting is one of the most beloved acts of worship to Allah ﷻ. The Prophet Muhammad ﷺ regularly fasted outside of Ramadan and encouraged the Ummah to do the same. He said: "Whoever fasts one day for the sake of Allah, Allah will keep his face away from the Hellfire by a distance of seventy years." (Sahih Bukhari and Muslim). Understanding the recommended fasting days helps you incorporate this powerful practice into your regular routine.
The most important Sunnah fasting days include: Mondays and Thursdays — the Prophet ﷺ said, "Deeds are presented on Monday and Thursday, and I like that my deeds be presented while I am fasting." The three white days (Ayyam al-Beed) — the 13th, 14th, and 15th of each Islamic (Hijri) month, named for the full moon that makes the nights bright. The Day of Arafah (9th Dhul Hijjah) — fasting this day expiates the sins of the previous year and the coming year for those not performing Hajj. The Day of Ashura (10th Muharram) — expiates the sins of the previous year, and it is Sunnah to fast the 9th along with it.
The Prophet ﷺ also fasted most of Sha'baan (the month before Ramadan) and recommended fasting six days of Shawwal (the month after Ramadan), saying: "Whoever fasts Ramadan then follows it with six days of Shawwal, it will be as if he fasted the entire year." The fast of Prophet Dawud (عليه السلام) — fasting every other day — was described by the Prophet ﷺ as the most beloved fasting to Allah.
The Sunnahs related to fasting include: having suhoor (pre-dawn meal) and delaying it as close to Fajr as possible; breaking the fast promptly at Maghrib with dates and water; saying the du'a when breaking the fast: ذَهَبَ الظَّمَأُ وَابْتَلَّتِ العُرُوقُ وَثَبَتَ الأَجْرُ إنْ شَاءَ اللَّهُ ("The thirst has gone, the veins are moistened, and the reward is confirmed, if Allah wills"); and making du'a at the time of breaking fast, as it is a time of accepted supplication.