Eid al-Ghadir is a Shi’a holiday that celebrates the appointment of Ali ibn Abi Talib, Prophet Muhammad’s cousin, and son-in-law, as the Prophet’s successor. The festival takes its name from the place where the Prophet Muhammad is believed to have made this announcement, the Pond (Ghadir) of Khumm. 

Eid al-Ghadir is the commemoration of Prophet Muhammad’s (saw) final sermon at Ghadir Khumm, which took place on the 18th of Dhu al-Hijjah, 10 AH. Shias celebrate this event as the basis for their acceptance of Imam Ali’s (as) succession to the Prophet.