The Chhath ritual of worshipping the Sun God, even finds its mention in the Mahābhārata when on sage Dhaumya’s advice, Draupadi performs similar rites to help the Pandavas regain their lost kingdom of Hastinapur. According to a folklore in the state of Bihar, there’s another history behind celebrating Chhath Puja.
It is believed that Lord Rama and Sita had kept fast and done a puja to please the Sun God after they had returned to Ayodhya from their 14 years exile.
On the first day of the Puja (Nahan Khan), the devotees take a dip in a river or a pond early in the morning and then carry some water home from the same water body to prepare prasad. They clean their houses and its surroundings and have only one meal on this day.
Day Two is called ‘lohanda’, and devotees on this day observe a fast from morning till sunset (having just one meal) before the tough task of 36-hour long no-food-no water fast begins.
One of the biggest reasons that Chhath has special place for a Bihari, is because Sita’s homeland Janakpur was located in the Mithila, a region which falls in Nepal and partially in Bihar, and this is where they believe Chhath Puja originated.