Kamika Ekadashi Vrat Katha, Story is given here. Kamika Ekadashi Vrat Katha is mentioned as a conversation between Lord Krishna and King Yudhishtira.
Kamika Ekadashi Vrat katha goes like this….
Yudhisthira Maharaj said, “Oh Sri Krishna, I would like to hear from You the glories of the Ekadashi that occurs during the dark fortnight (Krishna paksha) of the month of Shravana (July–August). Please be merciful to me and explain its glories.”
Sri Krishna, replied, “Oh King, please listen attentively as I describe the auspicious influence of this day, which removes all sins. Narada Muni once asked Lord Brahma about this same topic.
Lord Brahma replied, ‘My dear son Narada, for the benefit of all humanity I shall happily tell you everything you wish to know; for just hearing the glories of the Kamika Ekadashi bestows merit equal to that obtained by one who performs a horse sacrifice. Certainly, great merit is attained by one who worships, and who also meditates on the lotus feet of the four-armed Lord Gadadhara, who holds a conch shell, disc, club and lotus in His hands and who is also known as Sridhara, Hari, Vishnu, Madhava, and Madhusudana.
Observing Kamika Ekadashi bestows the same merit as donating a milch cow and her auspicious calf, along with their feed. On this all auspicious day, whosoever worships Lord Sri Sridhara-deva, Vishnu, is glorified by all the devas, Gandharvas, Pannagas, and Nagas.
Those who are afraid of their past sins and completely immersed in sinful materialistic life should at least observe this best of Ekadashis according to their ability and thus attain liberation. Oh Narada, Lord Shri Hari Himself once said about this Ekadashi, “One who fasts on Kamika Ekadashi attains much more merit than one who studies all the spiritual literatures.”
Anyone who fasts on this particular day and remains awake throughout the night will never experience the anger of Yamaraja, the king of death personified.
Whosoever worships Lord Shri Hari with Tulasi leaves is freed from all implication of sin. Indeed, he lives untouched by sin, as the lotus leaf, although in the water, is untouched by it.
The Supreme Personality of Godhead is more pleased by one who offers Him a single Tulasi leaf than by one who worships Him with pearls, rubies, diamonds, etc. One who offers Lord Keshava newly grown manjari buds from the tulasi plant gets rid of all the sins he has committed during this or any other lifetime. Indeed, mere darshana of Tulasi on Kamika Ekadashi removes all sins, and merely touching her and praying to her removes all kinds of disease. One who waters Tulasi devi need never fear the Lord of death, Yamaraja. One who plants or transplants Tulasi on this day will eventually reside with Lord Shri Krishna in His own abode. To Srimati Tulasi devi, who awards liberation in devotional service, one should therefore daily offer one’s full obeisances.
Even Chitragupta, Yamaraja’s secretary, cannot calculate the merit obtained by one who offers Srimati Tulasi-devi a perpetually burning ghee lamp. So dear is this sacred Ekadashi to the Supreme Personality of Godhead that all the forefathers of one who offers a bright ghee lamp to Lord Shri Krishna on this day ascend to the heavenly planets and drink the celestial nectar there. Whoever offers a ghee or sesame oil lamp to Shri Krishna on this day is freed from all his sins and enters the abode of Surya, the Sun-god, with a body as bright as ten million lamps. This Ekadashi is so powerful that if one who is unable to fast simply follows the practices as mentioned herein, he / she is elevated to the heavenly planets, along with all their forefathers.’
Oh Maharaj Yudhisthira, Lord Shri Krishna concluded, “…these were the words of Prajapati Brahma to his son Narada Muni concerning the incalculable glories of this Kamika Ekadashi, which removes all sins. This sacred day nullifies even the sin of killing a brahmana or the sin of killing an unborn child in the womb, and it promotes one to the spiritual world by making one supremely meritorious.”
Whosoever hears these glories of the Kamika Ekadashi with faith becomes free of all sins and returns home, back to Godhead.