Eid al-Ghadeer is an Islamic holiday observed by Shia Muslims worldwide on the 18th day of the month of Dhu al-Hijjah. It commemorates the appointment of Ali ibn Abi Talib as the successor of the Islamic prophet Muhammad, which took place at the pond of Khumm during Muhammad's Farewell Pilgrimage. This event is significant in Shia Islam as it marks Ali's designation as the first Imam after Muhammad. In contrast, Sunni Muslims do not recognize Eid al-Ghadeer as a celebratory day, leading to differing interpretations of Ali's role in Islamic history, which is a key factor in the division between Shia and Sunni denominations. Shia Muslims typically celebrate this day by taking a mass oath to reaffirm their commitment to Islam. In Iran, where Shia Islam is the official state religion, Eid al-Ghadeer is recognized as an official public holiday.