0511 GMT December 16, 2018
Iranian worshippers chant slogans urging unity of Islamic World.
Eid al-Adha also called the 'Festival of Sacrifice', is the second of two Islamic holidays celebrated worldwide each year (the other being Eid al-Fitr).
It honors the willingness of Ibrahim (Abraham) to sacrifice his son as an act of obedience to God’s command. Before Abraham could sacrifice his son, God provided a lamb to sacrifice instead.
In the Islamic lunar calendar, Eid al-Adha falls on the 10th day of Dhu al-Hijjah.