Khordad Sal is the birth anniversary of the Prophet Spitaman Zarathusatra (Zoroaster), who founded Zoroastrianism. Khordad Sal is celebrated on the sixth day of the Parsi month, Farvardin, by offering prayers at the temples. It falls sometime in August or September. There lies the difference in opinion about the eaxct year of Zarathushtra's birth. But it is generally accepted that he was born in the beginning of the first millennium BC.

Similarly, the day of his birth is also not precisely known, and the fixing of Khordad Sal as his birthday is symbolical.The religious lore and texts of the Parsis mention the festival and its importance. In some old Parsi texts, this day is also spoken of as the Navroz-I-Khas, which means 'special new year's day', while the real New Year's day is referred to as Navroz-I-Am, meaning 'common new year's day'.