The holiday occurs on the eighth day of the Islamic month of Rabi ul-Awwal, its date varying from year to year on the Gregorian Calendar.
Imam Hasan is regarded as the eleventh imam of the Shia branch of Islam. He is seen as one of the most important successors of Muhammad, both in a spiritual and political sense.
Imam Hasan was born in A.D. 846 and was the son of the tenth imam. When his father was suspected as a conspirator against the sitting Caliph in Medina, his father soon turned up dead. Thereupon, Hasan was shipped off to Samarra to be kept there under arrest so he would not later try to spread Shia Islam in Medina, a Sunni caliphate.
Imam Hasan pored over the Koran and over Sharia law while in “captivity” and is also thought to have studied various other languages, including Persian.
But only six years after his father died, Imam Hasan was poisoned to death. His son Muhammad al-Madhi is considered his successor under Shia Islam. And the Birthday of Imam Madhi is also a public holiday in Iran.