When Does The Fasting Of Ashuraah Begin

Question:

When does the fasting of Muharram begin or the fasting of 'Aashooraa begin? Does the fasting begin on the first day of Muharram or in the middle of the month or the end of the month? And how many days are to be fasted, because I heard that the fasting begins from the first of Muharram until the tenth? May Allaah grant you success.

Ibn Baaz (rahimahullaah) answered: 

The Prophet (salallaahu alaihi wassallam) said: "The best fasts after Ramadaan are in the month of Allaah: al-Muharram." And that is 'Aashooraa. And the meaning is that he fasted it all, from the first day till the last, from the beginning till the end. This is the meaning of the hadeeth. However, he specified from this month, the 9th and the 10th day, or the 10th and the 11th day for the one who is not able to fast the whole month. 

The Messenger (salallaahu alaihi wassallam) would fast 'Aashoorah in the days of Jaahiliyyah [prior to Revelation], and the people of Quraish would also fast it. Later on when the Messenger (salallaahu 'alaihi wassallam) arrived in Madeenah, he found that the Jews were also fasting it. So he asked them concerning it, so they replied: "It is the day on which Allaah saved Moosaa and his people, and He destroyed the Pharaoh and and his people, so Moosaa fasted it in gratitude to Allaah, so we likewise fast it." Allaah's Messenger (salallaahu 'alaihi wassallam) said: "We have more right with respect to Moosaa and are more deserving of him." So he (salallaahu 'alaihi wassallam) fasted and he commanded that it be fasted. So it is a Sunnah (recommended) to fast the Day of 'Aashoorah (10th Muharram) and it is from the Sunnah to fast the day before it or the day after, due to what is narrated from him (salallaahu 'alaihi wassallam), "Fast the day before it and the day after it." In a wording there occurs: "A day before it or a day after it." And in another narration: "If I live till next year, I will surely fast on the ninth," meaning along with the tenth - and this is best, that a person fasts the tenth because that is a great day, wherein goodness was attained for Moosaa (alaihi salaam) and the Muslims with him, and our Prophet (salallaahu 'alaihi wassallam) fasted that day - so we fast the ninth with our Prophet in acting upon his legislation (salallaahu 'alaihi wassallam). And we can fast along with the tenth, the day before it or the day after in order to differ from the Jews. And the best way is to fast the ninth and the tenth due to the hadeeth: "If I live till next year, I will surely fast the ninth." So if a person was to fast the tenth and the eleventh, or all three days: the ninth, tenth and eleventh, it is all good - and in that there is a differing from the Jews. And if one was was to fast the month, then that is more more virtuous for him. 

Source: http://www.binbaz.org.sa/mat/13761

Translated: Abu Khadeejah Abdul-Waahid