This day in particular, and this month in general, have a number of significances for both Sunni and Shia Muslims. Muharram is the month during which the Prophet Muhammad emigrated from Mecca to Medina, the event which marked the beginning of the Muslim calendar and the founding of the first Islamic city-state in Medina. Ashura is the day that God saved Moses and the Children of Israel from the bondage of Egypt. The Prophet encouraged Muslims to fast this day (and the day before) in gratitude to God, just as Moses did thousands of years before.
The fast of Ashura is not obligatory. Nevertheless, fasting during Ashura is greatly encouraged and handsomely rewarded by God. It is significant, and fascinating, that the faithful of one major religion, Islam, perform extra acts of worship in gratitude to God for one of the most important events in the sacred history of another major world religion, Judaism.
Ashura is also important because of an event 61 years after the Prophet's migration. On the day of Ashura in the Iraqi city of Karbala, the grandson of Prophet Muhammad (peace be upon him), Husayn, was murdered along with 72 of his kinsmen by the army of the Muslim Caliph Yazid. This day is probably the most important day in all of Shia Islam, and Shia Muslims have been known to self-flagellate in mourning of the Imam's murder
That a certain old woman came to the Prophet and requested him to pray to Allaah to make her enter paradise. The Prophet said, 'O mother of so and so! No old woman shall enter into paradise'. The narrator says that on hearing this the old woman went back weeping. The Prophet said to the people around him to go and tell the old woman that she would not enter into paradise as an old woman. (Tirmidhi) Then he recited the verse:
"Verily we! We have created those (maidens) by a creation and have made them virgins, loving, of equal age" Qur'aan 56: 35-37