Fasting the day of ‘Ashoora’ does expiate for the past year. The Prophet ﷺ said: “Fasting the day of ‘Arafah I hope Allah will expiate thereby for the year before it and the year after it,and fasting the day of ‘Ashoora’ I hope Allah will expiate thereby for the yearthat came before it”, Narrated by Muslim, 1162. This is by the bounty that Allah bestows upon us, whereby fasting one day expiates for the sins of an entire year. And Allah is the Owner of great bounty.
The Prophet ﷺ used tobe very keen to make sure he fasted on the day of ‘Ashoora’ because of itsgreat status. It was narrated that Ibn ‘Abbaas (may Allah be pleased with him)said: “I never saw the Prophetﷺ so keen to make sure he fasted anyday and preferring it over another except this day, the day of ‘Ashoora’, andthis month – meaning Ramadaan”, Narrated by al-Bukhaari, 1867.
What is meant by being keen to make sure he fasted it is to earn itsreward.
With regard to the reason why the Prophet ﷺfasted on the day of ‘Ashoora’ and urged the people to do likewise is mentioned in the hadeeth narrated by al-Bukhaari (No. 1865) from Ibn ‘Abbaas (may Allah be pleased with him), who said: The Prophet ﷺcame to Madeenah and saw the Jews fasting on the day of ‘Ashoora’. He said,“What is this?” They said, “This is a good day, this is the day when Allah saved the Children of Israel from their enemy and Moosa fasted on this day.” He said, “We are closer to Moosa than you.” So, he fasted on this day and told the people to fast.
The words “this is a good day” – according to a version narrated by Muslim, “This is a great day when Allah saved Moosa and his people and drowned Pharaoh and his people.” The words “so Moosa fasted on this day” – Imam Muslim added in his report: “In gratitude to Allah, so that is we fast on this day.”. According to another version narrated by al-Bukhaari, “So we fast it out of respect forit.”
The words “and told the people to fast” – according to another version narrated by al-Bukhaari, “He said to his companions, ‘You are closer to Moosa than them, so fast this day.”
The expiation of sins that is achieved by fasting ‘Ashoora’ refers to minor sins; with regard to major sins, they need separate repentance.
Al-Nawawi (may Allah have mercy on him) said: “Fasting the day of Arafaah expiates for all minor sins, in other words this brings forgiveness for all sins except for major sins”
Then he said:
“Fasting the day of ‘Arafaah is an expiation for two years, and the dayof ‘Ashoora is an expiation for one year, and if a person’s Ameen coincides with the Ameen of the angels, his previous sins will be forgiven… Each of the things mentioned may bring expiation. If he does something that expiates for minor sins he will be expiated, and if there are no minor or major sins, it will be recorded for him as good deeds and he will rise in status thereby… If there is one or more major sins and no minor sins, we hope that it will reduce his major sins”, Al-Majmoo’ Sharh al-Muhadhdhab, part 6.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: “The expiation of purification, prayer, and fasting Ramadaan, ‘Arafah and ‘Ashoora’ applies to minor sins only”, Al-Fataawaal-Kubra, part 5.