Pandav Bhima Ekadashi, also known as Nirjala Ekadasi, falls on the 11th day of the Shukla Paksha in the Jyeshta month (May – June). The story of Pandav Bhim Ekadasi is associated with Bhima, the second Pandava brother. The importance of Pandav Bhim Ekadasi is mentioned in the Brahmavaivarta Purana. In 2012, Nirjala Ekadasi is observed on May 31 (in some regions) and June 1 (in majority of regions).
The four Pandava brothers – Yudhisthira, Arjuna, Nakula, Sahadeva – Kunti, mother of the Pandavas, and Draupadi, the wife of the Pandavas, used to observe Ekadasi fasting without fail. Bhima, the second of the Pandavas, used to never fast as he could not control his hunger. He always had a guilt feeling of not observing the Ekadasi Vrat.
Once Bhima asked Veda Vyasa, who is also the grandfather of the Pandavas, to help in observing the Ekadasi Vrata. He said that Yudhishitra, his eldest brother, always asks him to observe fasting. He is ready to pray and give charity and observe all the rules but not fasting. And if there is no other way out he is ready to fast on one Ekadasi out of the 24 Ekadashis.
Sage Vyasa then suggested that he can observe the Ekadasi which occurs during the waxing moon in the month of Jyeshta (May – June) during the sun’s presence in either Taurus or Gemini Rashi is called Nirjala Ekadasi. One should observe total fast and should not even drink water.
Observing this Ekadasi is equal to observing all the 24 Ekadashis.
From that day onward Bhimasena began observing Nirjala Ekadasi and it came to be known as Pandava Nirjala, or Bhimseni Ekadasi.