Religious festival of Islam, celebrated on the 10th day of the Muslim month of Muharram (see more on Muslim Calendar).
For Shi'i Muslims the Ashura is celebrated as the most important day of the longer Muharram festival. Their Ashura festival commemorates the death of Husayn in 680 in his fight to get control of the Caliph position against Caliph Yazid. For Shi'is, the Ashura is a day of great mourning, and strong emotions are expressed in the many rituals and activities connected to this day.
The most visual of these celebrations is the flagellation by male Shi'is. Whips, often with sharp ends, or even small knives are used to make their backs bleed. The reason for this ritual is that only physical pain can truly reflect the pain of the Muslim world when Husayn died, and Ali's family's fight to lead the Muslim world came to an end. This flagellation ritual is, however, just a part of a complex ritual in which the Shi'is commemorate every stage of the preparation for the battle, and the battle itself.
Ashura is not limited to Shi'is alone, however. It is also celebrated among Sunni Muslims, although for very different reasons. The intensity cannot be compared to the Shi'i rituals, and it is not a central ritual in Sunni Islam.
It is commendable, but not compulsory, for all Sunnis to fast on Ashura, and all the devout will do so. The day is considered to be the celebration of different historical incidents, like the day that Noah left the Ark. In Mecca, the Ka'ba is opened for visitors on this day.
There are two variant explanations for Ashura's historical background. The one of Western scientists traces it back to Muhammad's arrival in Yathrib (later Madina) and the influence from the Jews in this town. On the day of Atonement 'ashor, the Jews fasted from sunset to sunset (24 hours), which was different from other fast days that took place only during daytime. The Jews celebrated Ashor on the 10th Tishri (today Yom Kippur). Muhammad adopted this practice, as well as many other Jewish rituals.
But in 624 (2 AH) Muhammad's relations with the Jews soured, and the Muslims stopped acknowledging Ashor, and moved the fast to the month of Ramadan (sawm). The Ashor fast was no longer a religious duty.
According to the Muslim traditions on the other hand, Ashura can be traced back to ancient Arab times and Ibrahim. Muhammad brought the tradition back to its pristine purity and correct practice.