Muslim mentioned on the authority of Abu Qatada that the Messenger of God, may God’s prayers and peace be upon him, said about fasting on the day of Ashura, he hoped that God would atone for the year before it

So the movement of his day was equal in strength to the strength of the days of the entire year if treated as every day. With what is appropriate for him in the form of worship, fasting is forbidden by his own strength from the one who fasted on behalf of all that he committed in the previous year, so he will not be held accountable for anything that he committed during Ramadan and other virtuous days and nights, even though Ramadan is better than it, as well as the Day of Arafah, the Night of Destiny, and Friday.