Ashura is an important occasion in the Islamic calendar, especially for Shia Muslims. Here are the main things to know about Ashura:

• Date: Ashura falls on the 10th day of Muharram, the first month of the Islamic lunar calendar. Muharram is a month of mourning for Shia Muslims.

• Origin: Ashura commemorates the death of Imam Husayn, the grandson of the Prophet Muhammad, at the Battle of Karbala in 680 CE. Husayn was killed along with his family and followers by the army of the ruler Yazid.

• Significance: The martyrdom of Husayn, who opposed the tyrannical Yazid, came to symbolize the struggle of truth against oppression. It plays a central role in Shia history, theology and identity.

• Commemoration: Shia Muslims commemorate Ashura through:

- Fasting: Shia Muslims often fast on Ashura as Husayn fasted on that day before the battle.

- Mourning: Husayn's death is mourned in majlis (congregation or gathering). People recite elegies and lamentations.

- Passion plays: Ritualistic reenactments of the Battle of Karbala retell the story of Husayn's sacrifice.

- Self-flagellation: Some Shia Muslims (especially Twelvers) practice self-flagellation to symbolize mourning Husayn's suffering.

• Sunni View: Though they revere Husayn, Sunnis do not emphasize Ashura in the same way as Shia due to differing interpretations of Islamic history. For them, Ashura is an optional, not obligatory, day of fasting.

So in short, Ashura commemorates the martyrdom of Imam Husayn - a pivotal event in Shia history - through fasting, mourning, passion plays and other rituals of remembrance. It symbolizes the struggle for righteousness and plays an important role in Shia Muslim piety and identity.

References

https://ahlalbayt.quora.com/https-www-quora-com-What-is-Ashura-How-is-Ashura-commemorated-answer-Mahdi-Chegini-1?ch=18&oid=122071009&share=5b1b9045&srid=hyfRI3&target_type=post