What is the ruling on singling out the month of Muharram for fasting like that of David (peace be upon him)?

The best fasting after Ramadan is Allah's month of Muharram, and the best prayer after the obligatory ones is the night prayer (Qiyam al-Layl). The fast of David is not necessarily perpetual; rather, it can be observed according to one's capacity, and whoever discontinues it will be rewarded for what they have already fasted. There is no harm in fasting the month of Muharram in the manner of David, for those who are able, provided that one does not believe there is a special virtue in doing so or make it an annual habit. One must be keen to fast the day of Ashura, even if it coincides with a day of breaking fast.