The ruling on fasting the day of 'Ashura alone.

Question:
What is the ruling on fasting the day of 'Ashura alone, and is it obligatory for a person to fast a day before it or a day after it, and what is the wisdom behind that?

Answer:
Answer: Ibn al-Qayyim (may Allah have mercy on him) mentioned in (Zad al-Ma'ad fi Hady Khayr al-'Ibad) that fasting the day of 'Ashura falls into three categories. The first category, which is the best of them, is to fast the three days: the ninth, the tenth, and the eleventh. This is the best. Next comes fasting the ninth and the tenth. Next comes fasting the tenth and the eleventh. All of them, praise be to Allah, have great virtue. If a person fasts the day of 'Ashura alone, this is permissible, but the Prophet (peace and blessings be upon him) said: "Differ from the Jews." The Jews fast the day of 'Ashura and say that it is the day in which Allah honored Musa (peace be upon him) and his people, and in which He destroyed Pharaoh and his people. So they used to fast it. The Prophet (peace and blessings be upon him) said: "We have more right to Musa than you do." So he fasted it and ordered its fasting along with fasting a day before it or a day after it, in order to differ from the Jews.