Nirjala Ekadashi is considered as the most austere and hence, most sacred of ekadashis. If observed religiously, it is said the most rewarding and granting the virtue gained by the observance of all 24 ekadshis in the year. Ekadashi Vrat is considered highly pious and is assumed to be one of the ways to attain Moksha.
Nirjala Ekadashi falls on the Shukla paksha in the month of Jyestha. It is also called "Jyeshtha Shukla Ekadashi" or "Bhimsaini Ekadashi". It is considered as one of the most rewarding fast.
The greatness of Nirjala Ekadasi was explained by Sage Vyas-
It is equal to going on pilgrimage.
It provides virtue of all 24 Ekadashi.
It washes away all sin.
It grants happiness, prosperity, longevity and moksha (salvation).
This Ekadasi happens before monsoon season and therefore it is also helps in cleansing the body.
Nirjala Ekadashi is also known as Pandava Bhima Ekadashi, or Pandava Nirjala Ekadashi. This name is derived from Bhima, the second and strongest of the five Pandava brothers, heroes of the Hindu epic Mahabharata. The Brahma Vaivarta Purana narrates the story behind the Nirjala Ekadashi vrata vow. Bhima, a lover of food, wanted to observe all ekadashi fasts, but could not control his hunger. He approached the sage Vyasa, author of the Mahabharata and grandfather of the Pandavas for a solution. The sage advised him to observe Nirjala Ekadashi, when for one day in the year, he should observe an absolute fast. Bhima attained the virtue of all 24 ekadashis, by observing Nirjala Ekadashi.
Determination of Date
Nirjala Ekadashi is celebrated on Jyeshtha Shukla Ekadashi falling at sun rise. If this Ekadashi falls at Sun rise on two days or does not fall during Sun Rise in that situation it is celebrated on the first day.
How to Celebrate
Nirjala means without water. Hence, fast is observed without water and food. It is considered as the most strict and hence, most sacred of all Ekadashis. This fast is extremely difficult to follow as it falls in the hot Indian summer. The 24 hours long fast begins from sunrise on Nirjala Ekadashi to sunrise the next day. People fast and offer puja to Lord Vishnu on this day.
The fast begins with Sandhyavandanam – a prayer. This prayer is performed in the evening before Nirjala Ekadashi, i.e. on 10th lunar day. After prayer devotee takes only one meal, without rice (as rice eating is prohibited). The strict fast continuous throughout Ekadashi. It gets over on next morning. Devotees offer prayer, tulsi, fruits, and sweets to Lord Vishnu and then finish their fast.
Offer Puja to Lord Vishnu and seek his grace.
Sprinkle Oanchamiritam on the idol of Lord Vishnu.
Wash with clean water and offer new clothes.
Offer flowers, incense, water, lamps and a hand fan.
In evening, worship Vishnu with Durva grass.
Visit nearby Vishnu temple and observe Jagran at night.
Chant bhajans, Vishnu Sahasranama and other slokas dedicated to Lord Vishnu
Donate clothes, food grains, umbrellas, hand-fans, pitchers filled with water, gold etc.