The story
The Pandavas, their mother Kunti and Draupadi all kept every Ekadashi. Only Bhima, whose body burned with the fire called Vrika that gave him his great strength and appetite, could not bear to go without food.
Troubled, Bhima went to the sage Vyasa and said: “My brothers tell me I will not reach heaven unless I fast. I can give charity and worship with all my heart, but I cannot fast even once a month, let alone twice. Is there a single vow that would be enough?”
Vyasa told him of the Ekadashi of the bright half of Jyeshtha, when the sun is at its fiercest. “On this day,” he said, “give up food and even water from sunrise until sunrise on Dwadashi. Water may touch your lips only for the ritual sipping (achamana). Whoever keeps this one fast gains the merit of all the Ekadashis of the year.”
Bhima kept the fast with great effort through the long summer day and night, and broke it the next morning after worship and gifts. From then on this Ekadashi came to be called Bhimaseni or Pandava Ekadashi.
Because the fast is kept in the hottest season, the day is also known for gifts of water: pots of cool water, fans, umbrellas, sherbet and fruit are given to others, and many set up water stalls for travellers.
Retold in our own words from the traditional story; versions told in families and booklets differ in details.