Parliament rests on Friday as its earlier schedule clashed with Chhath, a festival to hail the glory of Sun God which originated in central Bihar several centuries ago.
But what began as a 'little tradition' has now expanded to almost every place where the state's huge outwardly mobile population set its foot.
The banks of Yamuna and the beaches of Mumbai are no exception as millions of Bihar natives observe Chhath there, even though in later years the festival came to be associated with the river Ganga that divides Bihar in two parts, and the state's other rivers.
Sociologists said the festival's scale had grown as rapidly as the migrant population from Bihar, mainly because it offered people a chance to immediately associate with their roots and culture in a manner very different from other major occasions like Durga Puja, Diwali and Holi.
"The expansion of a group of people in newer and uncharted areas makes it more concerned about identity. Chhath becomes special because other festivals are not so well entwined with their place of origin, in this case Bihar.
The trend is same for India's other region-specific festivals but Chhath is highly visible as the sheer number of people celebrating it is huge in places like Delhi and Mumbai," JNU sociologist Anand Kumar said.
Natives of Bihar have moved out in large numbers during the past two decades in search of better livelihood prospects.
The otherwise rigorous festival -- in which those observing it fast for three days under a regimen aimed at not displeasing the Sun God -- has a liberal streak too.
The rituals involve paying homage by pouring milk before the setting Sun one day and to the rising Sun the next morning. It is now increasingly done by the side of other water bodies like oceans, lakes and ponds.