In the Fatimid era, Navroz was celebrated by the Imams and later in history when the Imams lived in Iran, this holiday became an important Ismaili holiday.
“Morale and enthusiasm were kept up by the observance of various festivals of general Islamic nature; particularly those of Shia and Ismaili. Fridays and the two Idd days were the days of festivity. Moreover, the Shia festival of Idd-e-Ghadeer al-Khumm and the 10th of Muharram were also observed.
Birthdays of the Ahl-e-Bayt (the Prophet’s family) and the Imams and certain important dates of the year were celebrated. Imam took part in the celebrations of the festivals. Local festivals of secular origin, like the “Flooding of the Nile” and “Navroz” (beginning of spring) were also encouraged by the Imam. Imam al-Muiz would hold huge receptions at his palace; processions were taken through the town and the whole town was illuminated”.