The glories of Parsva Ekadasi, which is also known as Parivartini Ekadasi or Vamana Ekadasi are described in Brahma-vaivarta Purana in the conversation between Lord Krsna and Maharaja Yudhisthira.

Maharaja Yudhisthira asked Lord Krsna, “What is the name of the Ekadasi that occurs during the waxing moon in the month of August/September? How one should observe this Ekadasi, and what is the merit one obtains by observing it? Please explain to me all these in detail.

Lord Krsna replied, “O King! The Ekadasi that occurs during the waxing moon in the month of August/September is called Parsva Ekadasi. This Ekadasi is very auspicious. It awards one liberation and takes away all one’s sins. Just by hearing the glories of this Ekadasi, all the sinful reactions of a person are vanquished. The piety one obtains by observing this Ekadasi cannot be obtained even by performing a Vajapeya sacrifice. This Ekadasi is also know a Jayanti Ekadasi. One who worships Lord Vamana Deva with devotion on this day is worshiped by the inhabitants of the three worlds. A person who worships the lotus-eyed Lord Visnu with a lotus flower undoubtedly goes back to the abode of the Lord. On this Ekadasi the sleeping Lord turns from left side to right side. Therefore this Ekadasi is known as Parsva Parivartini (“changing sides”) Ekadasi.

Maharaja Yudhisthira said, “O Janardana! Inspite of hearing Your description, I still have some doubts. O Lord of Lords! How do You sleep, and how do You change sides? What are the procedures for observing the vow of Caturmasya? What should people do when You are sleeping? Why did You bind Bali Maharaja with ropes? O my Lord? Please describe all this to me in detail and remove my doubts?

Lord Krsna replied, “O lion-like King! In Treta-yuga there was a great devotee of Mine named Bali. Although born in a demoniac family, he regularly worshiped Me and offered Me various prayers. He also worshiped the brahmanas and performed sacrifices. Soon he became so prominent that he defeated Indra, the King of Heaven and conquered the heavenly planet. The Indra along with the other demigods and the sages approached Me. By their prayer I assumed the form of a dwarf (Vamana) and went to the sacrificial arena of King Bali dressed as a small bramacari.

“I asked Bali for three steps of land in charity. When Bali requested Me to ask for something more than simply three steps of land, I exhibited My determination to remain satisfied with what I had asked for. Without further consideration, King Bali and his wife, Vindhyawali, gave Me the three steps of land in charity. Due to being the Supreme Personality of Godhead, Lord Vamanadeva gradually began to expand His body. With one step He covered the seven lower planetary systems, and with His second step He covered the entire planetary systems including the sky. When Vamanadeva asked for a place to set His third step, King Bali, with folded hands, offered his own head. The Lord Vamanadeva placed His third step on the head of King Bali. Being fully satisfied by his humility, I blessed him that I would constantly live with him.

“On the day of this Ekadasi, which occurs during the waxing moon in the month of August/September, a deity form of Vamanadeva was installed in the residence of King Bali. Another form of Mine has been established in the bed of Ananta Sesa in the ocean of milk. The Supreme Lord sleeps for four months beginning from Sayana Ekadasi up to Utthana Ekadasi. One should offer special worship to the Lord during these four months. One should properly observe each and every Ekadasi.

By observing this Ekadasi, one obtains the result of performing one thousand horse sacrifices.