From the epics · 2 tellings · East India, North India
The armour Karna cut away (Karna, the Sun's son)
Karna, the Sun's son, was born in armour no weapon could pierce and never refused a Brahmin at the hour of his worship. The Sun warns him in a dream that Indra will come begging for it; Karna will not refuse, but asks for Indra's spear in return and cuts off his armour smiling. Bihar says Karna, king of Anga, was the first to keep Chhath, standing in the river to pray to his father.
Karna, son of the Sun and Kunti, born in armour and earrings, worships the Sun in the water every day and gives the Brahmins whatever they ask at that hour. The Sun comes to him in a dream as a Brahmin and warns him that Indra will beg for the armour. Karna says he would rather die with fame than live with a lie. The Sun tells him to ask for Indra's infallible dart in exchange. Indra comes as a Brahmin; Karna knows him, asks for the dart, and is given it for one use. He cuts the armour from his body, smiling, and the gods drop flowers. He is called Vaikartana.
Karna, made king of Anga, walks into the Ganga each morning until the water reaches his waist and offers water to the rising Sun for hours. Then he gives gold to all who ask, at Karna Chaura on the hill of Munger. Bihar says Chhath began with him, and the women who keep it stand in the river as he did.
What is different here:
Set in Anga; makes Karna the first to keep Chhath.
Sources: The Mahabharata, tr. Kisari Mohan Ganguli, Book 3, Vana Parva, Kundalaharana Parva (sections 299 to 309), and Adi Parva 111; Karna and Chhath in Bihar (Satmarg Astro; Svastika)