Karva Chauth vrat katha, story or legend about Karwa Chauth, is very important to read at the time of Karva Chauth puja. According to the legend, a woman named Karva was very much devoted to her husband.
One day, when he was bathing in river, her husband was caught by a crocodile. Seeing that, Karvas face became red and tied the crocodile with a cotton yarn and taken away that crocodile to Yama lok. Karva requested Lord Yama to curse the crocodile and send it to Narak (hell).
But, Yama was refused and scolded karva harshly. This incident made Karva to warn Yama that she will curse him. Yama afraid with her devotion towards her husband since he knows how powerful a devoted wife would be. He sent the crocodile to Narak. And he also blessed Karva’s husband with long life and prosperity.