Bhadrapada maas ke Shukla paksha ki is Ekadashi ko, Chaturmas ki yoga-nidra mein leen Bhagwan Vishnu Ksheersagar mein apni karvat (parsva) badalte hain — isiliye ise Parsva ya Parivartini Ekadashi kehte hain. Is din Bhagwan ke Vamana avataar ki pooja ka vishesh mahatva hai, isliye ise Vamana Ekadashi bhi kaha jaata hai.
Katha ke anusaar Prahlad ke vanshaj, daanveer aur balshali raaja Bali ne apne tap aur paraakram se teenon lok jeet liye the. Indra sahit devta swarg se khaded diye gaye aur sankat mein Bhagwan Vishnu ki sharan mein gaye. Devtaon ki raksha ke liye Bhagwan ne Vamana (ek bauna Brahmin baalak) ka roop dhaaran kiya.
Bali ek vishaal yagya kar raha tha, jahaan woh sab ko manchaaha daan de raha tha. Vamana-roopi Bhagwan vahaan pahunche aur Bali se keval "teen pag bhoomi" daan mein maangi. Bali ke guru Shukracharya ne sachetar kiya ki yeh svayam Vishnu hain, par daanveer Bali apne vachan se peeche na hata aur sankalp ka jal chhod diya.
Tabhi Vamana ne apna vishaal Viraat-roop dhaaran kiya — ek pag mein sampoorn prithvi aur dvitiya pag mein sampoorn swarg-lok naap liya. Jab teesre pag ke liye sthaan na bacha, to satyavaadi Bali ne apna mastak aage kar diya. Bhagwan ne teesra pag Bali ke sir par rakhkar use paatal-lok ka raaja banaaya. Bali ki is achal daan-sheelta aur samarpan se prasann hokar Bhagwan svayam uske dwaarpaal bankar uske paas rehne lage.
Seekh: Parsva (Parivartini / Vamana) Ekadashi sikhaati hai ki sachhi daan-sheelta, vachan-paalan aur sampoorn samarpan se manushya Bhagwan ki kripa ka adhikaari ban jaata hai — ahankaar nahi, vinamr samarpan hi Bhagwan ko priya hai.