ashura

The incident took place during Ashoura commemorations, when hundreds of thousands of people converge on the city of Karbala.
Ashura, the tenth day of the month of Muharram in the Islamic calendar. A time of rejoicing and deliverance, yet a time of grief and sorrow. From both the Sunni and Shi'a traditions, this day holds very significant to many.
You have never truly heard of Hussein, Karbala, or Ashura, and you probably didn't need to. No, this time in Islamic and global history never meant anything, until now.
Some Shiite leaders urge blood drives on Ashura, instead.