The colour white is often believed to symbolize purity and peace. Many Muslims wear the colour white when they attend Friday prayers. The colour black is considered the colour of mourning in Western and Mediterranean countries; however, it is considered a colour of modesty in some Muslim cultures. It is often worn by Shi'ite Muslims, who mourn the death of Husayn ibn Ali, killed at the Battle of Karbala. It is the colour of the chador worn by devout Iranian Shi'ite women and of the cloaks worn by the Ayatollahs, the Shi'a clergy. In many Shi'a countries, a black turban is worn only by male sayids, men who descend from Muhammad through his daughter Fatimah and his son-in-law Ali. In Sunni tradition, Muhammad wore a white kufi (head cap) with a black mana (turban).