Almighty Allah states in the Holy Quraan:
“It is the day of ‘Ashura. Allah has not made fasting obligatory for you. But I am fasting. He who likes to observe fast among you should do so, and he who likes not to observe it (does not have to) observe it.” Abu Qatada relates that the Holy Prophet (Sallallahu ‘alayhi wa Sallam) said that the fast on the 10th of Muharram atones for the sins of the preceding year.
Almighty Allah states in the Holy Qur’an:
“Four of them (Zul-Qa’dah, Zul-Hijjah, Muharram and Rajab) are sacred.”
The Month Of Muharram (The New Year OF Islaam):
The new year in Islam starts With the sighting of the new moon of Muharram. The primary month Muharram, is a month of great reward and virtue. Muharram itself implies `sacred‘ and is from those months which have been specified as holy in the Holy Quraan.
(10th Muharram) The Day of Ashura :
Despite the fact that the month of Muharram is a holy month all in all, the tenth of Muharram is the most sacred among every one of its days. The day is named ‘Ashura’. It is a the most essential and favored days of Allah in the Islamic calendar.
As indicated by the Holy companion, Ibn Abbas Radhiyallaahu Anhuma, when the Holy Prophet Sallallaahu Alayhi Wa Sallam moved to Madinah, he found that the Jews of Madinah used to fast on the tenth day of Muharram. They said that it was the day on which the Holy Prophet Moosa Alayhis Salaam and his adherents crossed the Red Sea marvelously, and the Pharaoh was drowned in its water.
On listening to this from the Jews, the Holy Prophet Sallallaahu Alayhi Wa Sallam said,
“We are more closely related with Moosa than you.” So the Prophet Mohammed Sallallaahu Alayhi Wa Sallam educated the Muslims to fast on the day of Ashura”. (Abu Dawood)
As per another Hadith, it is more advisable that the fast of Ashura ought to be either gone before or succeeded by an additional fast.
It implies that one should fast two days: either on 9th and 10th of Muharram or the 10th and 11th.
The reason of this additional fast as specified by the Holy ProphetSallallaahu Alayhi Wa Sallam is that the Jews used to quick upon the arrival of Ashura alone, and the Holy Prophet Sallallaahu Alayhi Wa Sallam needed to recognize the Islamic-method for fasting from that of the Jews. In this way, he advised the Muslims to add another fast to the day of Ashura.