Parsva Ekadashi, also called Parivartini, is the Ekadashi of the bright half of Bhadrapada, the day Vishnu is said to turn on his side in his four-month sleep. Its katha is the story of Vamana, the small brahmin boy who asked King Bali for three steps of land and covered the worlds with them.
The dates of the coming Ekadashis, with Smarta and Vaishnava days, are on the Ekadashi dates page, and each day's page there gives the parana window for your city. This page tells the story.
The katha
Yudhishthira asked, "Madhava, what is the Ekadashi of the bright half of Bhadrapada called, and whose worship is done on it?"
Krishna said, "It is called Parsva, and also Parivartini, because on this day I turn over in my sleep. It is also called Vamana Ekadashi, for on it my Vamana form is worshipped. Let me tell you why."
In the Treta age there was an asura king named Bali, the grandson of the great devotee Prahlada. Bali was unlike the asuras before him. He was generous beyond measure, honoured the brahmins, kept his word, and worshipped Vishnu. Through great sacrifices and the strength of his army he conquered the earth, then the heavens, and Indra and the gods had to leave their home.
Aditi, the mother of the gods, grieved for her sons. She kept a long vow and prayed to Vishnu, and he promised to be born as her child. He came into the world as a tiny boy, a brahmin student with a deerskin, a water pot, an umbrella and a sacred thread, and he was called Vamana, the dwarf.
At that time Bali was holding a great sacrifice; in the Bhagavata's telling, on the bank of the Narmada. Any brahmin who came was given whatever he asked. Vamana walked into the sacrificial ground, and the whole assembly turned to look at the shining child.
Bali welcomed him, washed his feet and said, "Young brahmin, you honour my sacrifice. Ask for anything: cows, gold, villages, a palace."
Vamana smiled. "I need very little. Give me as much land as I can cover in three of my steps."
Bali laughed kindly. "That is a child's request. Ask for more."
"A person who is not content with three steps," said the boy, "will not be content with three worlds. Three steps are enough."
Bali's teacher Shukracharya drew him aside. "This is no ordinary boy. It is Vishnu himself, and he has come to take everything you have. Do not make this gift."
Bali thought for a moment and replied, "If the Lord himself has come to my door to ask, what greater fortune could there be? I have said yes. I will not take back my word." He took water in his hand and made the gift.
Then Vamana began to grow. He grew past the sacrificial hall, past the clouds, past the sun and the moon. With one step he covered the earth. With the second he covered the heavens, and his foot reached so high that, it is said, Brahma washed it, and the water became the Ganga. Then he turned to Bali. "Where shall I put the third step?"
Bali bowed his head to the ground. "Lord, I have nothing left but myself. Place your third step on my head."
Vishnu placed his foot on Bali's head, and the king sank gently down to Sutala, a realm of the netherworld more beautiful than heaven. Pleased with his humility, Vishnu gave him that realm to rule and promised that Bali would be Indra in a coming age. Bali asked one thing more: "Stay with me." Vishnu agreed to stand guard at his door.
Krishna said, "So from then on one form of mine stays with Bali, and another rests on Shesha in the ocean of milk. On this Ekadashi, as I sleep, I turn to the other side. Whoever worships Vamana on this day and keeps the fast honours all three worlds."
Reading the story calmly
Bali is sometimes remembered as a defeated enemy, but the katha does not tell it that way. He loses his kingdom and gains something greater: the Lord as his guard and companion. Kerala's Onam remembers the same king with deep love, as a just ruler who visits his people each year.
What the day is kept for
The day sits midway through Chaturmas, the four months that begin on Devshayani Ekadashi and end on Dev Uthani Ekadashi. People keep it for humility and for generous giving; the text says it brings the merit of great sacrifices and leads to Vishnu's abode, and families hold that as the story's promise.
How it is kept
Vishnu is worshipped as Vamana, and in many homes the next day, Vamana Dwadashi, is kept as his birth. In Rajasthan and Madhya Pradesh, as Jal Jhulni Ekadashi, Krishna's image is carried in a palanquin to water, rocked on it and brought home with songs. In some families curd and rice are given to brahmins after parana. The general order of the fast is on the Ekadashi puja vidhi page.
Neighbouring Ekadashis
The Ekadashi before this one is Aja Ekadashi, the story of Harishchandra, and the one after is Indira Ekadashi, kept in Pitru Paksha for the ancestors. For the tithi on any day in your city, see the panchang.