Narrated Ibn Abbas: When the Prophet came to Medina , he found (the Jews) fasting on the day of 'Ashura' (i.e. 10th of Muharram). They used to say: "This is a great day on which Allah saved Moses and drowned the folk of Pharaoh. Moses observed the fast on this day, as a sign of gratitude to Allah." The Prophet said, "I am closer to Moses than they." So, he observed the fast (on that day) and ordered the Muslims to fast on it. [Sahih Bukhari, Volume 4, Book 55, Number 609]
“This is a righteous day” – in a report narrated by Muslim, [the Jews said:] “This is a great day, on which Allaah saved Moosa and his people, and drowned Pharaoh and his people.”
“Moosa fasted on this day” – a report narrated by Muslim adds: “… in thanksgiving to Allaah, so we fast on this day.”
According to a report narrated by al-Bukhaari: “… so we fast on this day to venerate it.”
A version narrated by Imaam Ahmad adds: “This is the day on which the Ark settled on Mount Joodi , so Nooh fasted this day in thanksgiving.”
“and commanded [the Muslims] to fast on that day” – according to another report also narrated by al-Bukhaari: “He said to his Companions: ‘You have more right to Moosa than they do, so fast on that day.”
The practice of fasting on ‘Aashooraa’ was known even in the days of Jaahiliyyah, before the Prophet’s mission. It was reported that Aaishah (may Allaah be pleased with her) said: “The people of Jaahiliyyah used to fast on that day…”
Al-Qurtubi said: “Perhaps Quraysh used to fast on that day on the basis of some past law, such as that of Ibraaheem, upon whom be peace.”
It was also reported that the Prophet (peace and blessings of Allaah be upon him) used to fast on ‘Aashooraa’ in Makkah, before he migrated to Madeenah. When he migrated to Madeenah, he found the Jews celebrating this day, so he asked them why, and they replied as described in the hadeeth quoted above. He commanded the Muslims to be different from the Jews, who took it as a festival, as was reported in the hadeeth of Abu Moosa (may Allaah be pleased with him), who said: “The Jews used to take the day of ‘Aashooraa’ as a festival [according to a report narrated by Muslim: the day of ‘Aashooraa’ was venerated by the Jews, who took it as a festival. According to another report also narrated by Muslim: the people of Khaybar (the Jews) used to take it as a festival and their women would wear their jewellery and symbols on that day].
The Prophet (peace and blessings of Allaah be upon him) said: ‘So you [Muslims] should fast on that day.’” (Reported by al-Bukhaari). Apparently the motive for commanding the Muslims to fast on this day was the desire to be different from the Jews, so that the Muslims would fast when the Jews did not, because people do not fast on a day of celebration. (Summarized from the words of al-Haafiz Ibn Hajar – may Allaah have mercy on him – in Fath al-Baari Sharh ‘ala Saheeh al-Bukhaari).
Fasting on ‘Aashooraa’ was a gradual step in the process of introducing fasting as a prescribed obligation in Islam. Fasting appeared in three forms. When the Messenger of Allaah (peace and blessings of Allaah be upon him) came to Madeenah, he told the Muslims to fast on three days of every month and on the day of ‘Aashooraa’, then Allaah made fasting obligatory when He said (interpretation of the meaning): “… observing the fasting is prescribed for you…” [al-Baqarah 2:183] (Ahkaam al-Qur’aan by al-Jassas, part 1).
The obligation was transferred from the fast of ‘Aashooraa’ to the fast of Ramadaan, and this one of the proofs in the field of Usool al-Fiqh that it is possible to abrogate a lighter duty in favour of a heavier duty.
Before the obligation of fasting ‘Aashooraa’ was abrogated, fasting on this day was obligatory, as can be seen from the clear command to observe this fast. Then it was further confirmed later on, then reaffirmed by making it a general command addressed to everybody. It was reported from Ibn Mas’ood that when fasting Ramadaan was made obligatory, the obligation to fast ‘Aashooraa’ was lifted, i.e., it was no longer obligatory to fast on this day, but it is still desirable (mustahabb).
The virtues of fasting Aashooraa
Narrated Ibn Abbas: “I never saw the Prophet seeking to fast on a day more (preferable to him) than this day, the day of 'Ashura', or this month, i.e. the month of Ramadan.” [Sahih Bukhari, Volume 3, Book 31, Number 224]
The meaning of his being keen was that he intended to fast on that day in the hope of earning the reward for doing so.
The Prophet (peace and blessings of Allaah be upon him) said: “…For fasting the day of ‘Aashooraa’, I hope that Allaah will accept it as expiation for the year that went before.” [Sahih Muslim, Book 006, Number 2602]. This is from the bounty of Allaah towards us: for fasting one day He gives us expiation for the sins of a whole year. And Allaah is the Owner of Great Bounty.
Which day is ‘Aashooraa’ ?
Al-Nawawi (may Allaah have mercy on him) said: “ ‘Aashooraa’ and Taasoo’aa’ are two elongated names [the vowels are elongated] as is stated in books on the Arabic language. Our companions said: ‘Aashooraa’ is the tenth day of Muharram and Taasoo’aa’ is the ninth day. This is our opinion, and that of the majority of scholars. This is the apparent meaning of the ahaadeeth and is what we understand from the general wording. It is also what is usually understood by scholars of the language.” (al-Majmoo’)