Significance and legend
Krishna tells Yudhishthira, in a dialogue first spoken by Brahma to Narada, that the merit of Kamika Ekadashi exceeds that of bathing in the Ganga at Kashi, at Naimisharanya or at Pushkar, and equals the merit of giving a cow with her calf. A traditional story tells of a landowner, a proud and short-tempered man, who quarrelled with a Brahmin and in his anger struck and killed him. Overcome with remorse, he wished to perform the Brahmin's funeral rites, but the other Brahmins refused to accept food from him, since he bore the sin of brahmahatya.
Seeking a way to atone, he asked a sage, who told him to observe Kamika Ekadashi with complete devotion, worshipping Vishnu with tulsi leaves and keeping vigil through the night. He did so, and in a dream Vishnu appeared and told him that he was freed from his sin. The text emphasises the glory of tulsi on this day: even seeing, touching or watering the tulsi plant destroys sins, and worshipping Vishnu with tulsi is more meritorious than offering gold or pearls.
How Kamika Ekadashi is observed
Observers eat a single meal on Dashami and fast on Ekadashi, worshipping Vishnu as Shridhara with tulsi leaves, yellow flowers, ghee lamps and sesame. Lighting a ghee lamp before Vishnu throughout the night is praised in the scripture. The Kamika katha and the Vishnu Sahasranama are recited. On Dwadashi, after sunrise and within the parana window, the fast is broken with food offered to Vishnu, after giving charity.