Eid al-Zahra is a festival celebrated by some Twelver Shii Muslims in Iran, also known as Omar Koshan or Jashn-e Hazrat-e Zahra. It is held annually and begins on the 9th day of the month of Rabi al-Awwal of the Islamic year, lasting until the 27th of the same month. The festival originally commemorated the assassination of the second caliph Umar ibn al-Khattab by the Persian slave Abu Lulua Firuz. In its current form, it is a carnival-type of festival in which social roles are reversed and communal norms upturned.

According to some traditions, the 9th of Rabial Awwal is also known as Eid-e-Zahra, which is celebrated as the Greatest Eid in the sight of the AhlulBayt (peace be upon them) and those who love and follow them. It marks a turning point in the history of the AhlulBayt and their followers, and is a day of joy and happiness for the lovers of the AhlulBayt. The festival is named after Fatima al-Zahra, the daughter of the Prophet Muhammad, and is a day of celebration and rejoicing for the lovers of the AhlulBayt.

The hadith which speaks about this day refers to it as the ‘Greatest Eid’ in the sight of the AhlulBayt and those who love and follow them. It is a day of joy and happiness for the lovers of the AhlulBayt, and marks the beginning of the leadership of Imam Mehdi. The festival is celebrated by reciting duas and prayers, and is a day of remembrance and celebration for the followers of the AhlulBayt.