Nirjala Ekadasi, also known as Pandava Ekadashi or Bhimsena Ekadasi, is observed in Shukla Paksha of Jyeshta month. Nirjala Ekadasi vrat katha or legend of Nirjala Ekadashi is mentioned in the Padma Purana and Mahabharata.
As per the Mahabharata, once Bhimasena asked Sage Veda Vyasa about the importance and significance of Ekadasi fasting. Veda Vyasa explained him the benefits and merits of Ekadashi fasting.
Listening to that, Bhim told him that his brothers Yudhistira, Arjuna, Nakula and Sahadeva would observe the fast without any trouble but he cannot be able to observe fasting on 24 Ekadashi vrat throughout the year. Bhimsen asked Veda Vyasa to suggest only one day of fasting that can give him the result of 24 Ekadasi vrata.
On Bhimsen’s request, Veda Vyasa advised him to observe fasting on Jyeshta Shukla Ekadashi, also called as Nirjala Ekadasi, which can give him all the benefits and merits of 24 Ekadashi fasting. Bhimasen observed the Ekadasi without even drinking water. Because of this legend, Jyeshta Shukla Ekadashi is also named as Pandava Ekadashi or Bhimsen Ekadashi.