Abu Bakrah (may Allaah be pleased with him) reported that the Prophet (peace and blessings of Allaah be upon him) said: “The year is twelve months of which four are sacred, the three consecutive months of Dhu’l-Qa’dah, Dhu’l-Hijjah and Muharram, and Rajab Mudar which comes between Jumaada and Sha’baan.” (Reported by al-Bukhaari, 2958).

Muharram is so called because it is a sacred (muharram) month and to confirm its sanctity. Allaah’s words (interpretation of the meaning): “…so wrong not yourselves therein…” mean do not wrong yourselves in these sacred months, because sin in these months is worse than in other months. It was reported that Ibn ‘Abbaas said that this phrase (…so wrong not yourselves therein…) referred to all the months, then these four were singled out and made sacred, so that sin in these months is more serious and good deeds bring a greater reward.

The Virtue of observing more naafil fasts during Muharram

Abu Hurayrah (may Allaah be pleased with him) said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘The best of fasting after Ramadaan is fasting Allaah’s month of Muharram.’ ” (reported by Muslim, 1982).

The phrase “Allaah’s month”, connecting the name of the month to the name of Allaah in a genitive grammatical structure, signifies the importance of the month. Al-Qaari said: “The apparent meaning is all of the month of Muharram.” But it was proven that the Prophet (peace and blessings of Allaah be upon him) never fasted any whole month apart from Ramadan, so this hadeeth is probably meant to encourage increasing one’s fasting during Muharram, without meaning that one should fast for the entire month.

It was reported that the Prophet (peace and blessings of Allaah be upon him) used to fast more in Sha’baan. It is likely that the virtue of Muharram was not revealed to him until the end of his life, before he was able to fast during this month. (Sharh al-Nawawi ‘ala Saheeh Muslim).

‘Aashooraa’ in History

Ibn ‘Abbaas (may Allaah be pleased with him) said: “The Prophet (peace and blessings of Allaah be upon him) came to Madeenah and saw the Jews fasting on the day of ‘Aashooraa’. He said, ‘What is this?’ They said, ‘This is a righteous day, it is the day when Allaah saved the Children of Israel from their enemies, so Moosa fasted on this day.’ He said, ‘We have more right to Moosa than you,’ so he fasted on that day and commanded [the Muslims] to fast on that day.” (Reported by al-Bukhaari, 1865). “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.’ ”

It is mustahabb (encouraged) to fast Taasoo’aa’ with ‘Aashooraa’

‘Abd-Allaah ibn ‘Abbaas (may Allaah be pleased with them both) said: “When the Messenger of Allaah (peace and blessings of Allaah be upon him) fasted on ‘Aashooraa’ and commanded the Muslims to fast as well, they said, ‘O Messenger of Allaah, it is a day that is venerated by the Jews and Christians.’ The Messenger of Allaah (peace and blessings of Allaah be upon him) said, ‘If I live to see the next year, in sha Allaah, we will fast on the ninth day too.’ But it so happened that the Messenger of Allaah (peace and blessings of Allaah be upon him) passed away before the next year came.” (Reported by Muslim, 1916).

Al-Shaafa’i and his companions, Ahmad, Ishaaq and others said: “It is mustahabb to fast on both the ninth and tenth days, because the Prophet (peace and blessings of Allaah be upon him) fasted on the tenth, and intended to fast on the ninth.”

On this basis it may be said that there are varying degrees of fasting ‘Aashooraa’, the least of which is to fast only on the tenth and the best of which is to fast the ninth as well. The more one fasts in Muharram, the better it is.

http://www.sunnahonline.com/ilm/sunnah/0018.htm