The Legitimacy of Fasting the Day of Ashura

Question:
Your Eminence the Shaykh, may Allah preserve you, the people of creed always and forever rejoice in the noble times and take from them admonition, wisdom, and a lesson. How is that to be, and we are in this noble month, the month of Allah, Muharram, and also close to the Day of Ashura? How do we make the most of that?

Answer:
Yes, these are great seasons that pass us by, so it is obligatory for us to seize them for ourselves and to do what Allah has prescribed in them. Among that is the Day of Ashura, for it is prescribed to fast it; it is recommended to fast it, and it expiates the sins of the previous year.
And in it is a great virtue, but it is not to be fasted alone; rather, a day before it or a day after it is to be fasted, as the Prophet (peace and blessings be upon him) commanded that. This day is the day in which Allah honored Musa and gave him victory over his people, and He drowned Fir'awn and his people. So Musa (peace be upon him) fasted it in gratitude to Allah, and we fast it in gratitude to Allah for the victory of the truth, because the victory of the truth at any time is among the good for the Muslims in every time and place. The Prophet (peace and blessings be upon him) fasted it, commanded its fasting, and commanded the fasting of a day before it in opposition to the Jews.
Because the Jews fast the Day of Ashura, so we oppose them by fasting a day before it or a day after it. This is what is prescribed and recommended. Yes.