Significance and legend
Parsva means side, and Parivartini means turning. On this Ekadashi, midway through Chaturmasa, Lord Vishnu is said to turn from his left side to his right in his yoga nidra. In the Brahmavaivarta Purana dialogue, Krishna tells Yudhishthira the story of King Bali, the virtuous grandson of Prahlada, who conquered the three worlds through his power and generosity. Indra and the gods, deprived of their realm, appealed to Vishnu.
Vishnu was born as Vamana, the dwarf son of Aditi and Kashyapa, and came to Bali's sacrifice to ask for three steps of land. Despite his guru Shukracharya's warning, Bali granted the request. Vamana grew into the cosmic Trivikrama, covered the earth and heavens in two strides, and Bali offered his head for the third. Pleased by Bali's integrity and devotion, Vishnu sent him to rule the netherworld and promised to remain with him. Krishna declares that one who worships Vamana on this Ekadashi worships the three worlds, and the day is also called Vamana Ekadashi.
How Parsva Ekadashi is observed
Devotees fast and worship Vishnu in his Vamana form with tulsi, lotus and other flowers, curd rice and charity of food. In Rajasthan and Madhya Pradesh the day is called Jaljhulani Ekadashi, when images of Krishna are carried in decorated palanquins to lakes and rivers. Reading the Vamana story, chanting and night vigil complete the observance. The fast is broken on Dwadashi after sunrise within the parana window, avoiding Hari Vasara.