Yudhishthira Maharaja said, "O Janardana, what is the name of the Ekadashi that occurs during the light fortnight of the month of Vaishakha (April-May)? What is the process for observing it properly?"
Lord Sri Krishna replied, "What Vasishtha Muni once told Lord Ramachandra I shall now describe to you. Lord Ramachandra asked Vasishtha Muni, 'O great sage, I would like to hear about the best of all fasting days – that day which destroys all kinds of sins and sorrows. I have suffered long enough in separation from My dear Sita, and so I wish to hear from you about how My suffering can be ended.'
Sage Vasishtha replied, 'O Lord Rama, You have questioned me in order to benefit all of humanity and fulfill everyone's desires. That day is Vaishakha-sukla Ekadashi, which falls on Dvadashi. It removes all sins and is famous as Mohini Ekadashi. The merit of this Ekadashi frees the fortunate soul from illusion. Therefore, if You want to relieve Your suffering, observe this auspicious Ekadashi perfectly, for it removes all obstacles from one's path and relieves the greatest miseries. If one even just hears about this auspicious Ekadashi, the greatest sins are nullified.
"On the banks of the Sarasvati river there was once a beautiful city named Bhadravati, which was ruled by King Dyutiman. O Rama, that steadfast, truthful, and highly intelligent king was born in the dynasty of the moon. In his kingdom was a merchant named Dhanapala, who possessed a great wealth of food grains and money. He was also very pious. Dhanapala arranged for lakes to be dug, sacrificial arenas to be erected, and beautiful gardens to be cultivated for the benefit of all the citizens of Bhadravati. He was an ardent devotee of Vishnu and had five sons: Sumana, Dyutiman, Medhavi, Sukruti, and Dhristabuddhi.
Unfortunately, his son Dhristabuddhi was always engaged in greatly sinful activities, he enjoyed illicit sex, gambling, and many other varieties of sense gratification. He disrespected the demigods; brahmanas; forefathers and other elders; and his family's guests. He spent his father's wealth indiscriminately, always feasting on untouchable foods and drinking wine to excess.
One day Dhanapala kicked Dhristabuddhi out of the house after he saw him walking along the road arm-in-arm with a prostitute. From then on, all Dhristabuddhi’s relatives were highly critical of him and distanced themselves from him. After he had sold his ornaments and become destitute, the prostitutes also abandoned him because of his poverty.
Dhristabuddhi was now full of anxiety, and also hungry. He thought, "What should I do? How can I maintain myself?" He then began to steal. The king's constables arrested him, and after whipping him, they warned him, "O evil one! There is no place for you here."
However, he entered the dense forest. He wandered here and there, hungry and thirsty and suffering greatly. Eventually he began killing lions, deer, boars, and wolves for food and thus his sins mounted day by day. On account of his previous sins, he was now immersed in an ocean of great sin.
Dhristabuddhi was always miserable and anxious, but one day, during the month of Vaishakha, by the force of some of his past merit he chanced upon the sacred ashrama of Kaundinya Muni. The great sage had just finished bathing in the Ganges river, and water was dripping from him. Dhristabuddhi had the great good fortune to touch some of those drops falling from the sage's clothes. Instantly Dhristabuddhi was freed of ignorance, and his sinful reactions were reduced. Offering his humble obeisances to Kaundinya Muni, Dhristabuddhi prayed to him with joined palms: "O great brahmana, please describe some kind of atonement I may perform without too much endeavor. I have committed so many sins in my life, and these have now made me very poor."
The great rishi replied, "O son, listen with great attention, for by hearing me you will become free of all your remaining sins. In the light fortnight of this month, Vaishakha, there occurs the sacred Mohini Ekadashi, which has the power to nullify sins as vast and weighty as Mount Sumeru. If you follow my advice and faithfully observe a fast on this Ekadashi, which is so dear to Lord Hari, you will be freed from all the sinful reactions of many, many births."
According to the sage's instructions, by fasting completely on Mohini Ekadashi, the once-sinful Dhristabuddhi became sinless. Afterwards he achieved a beautiful transcendental form and, free at last of all obstacles, rode upon Garuda, the carrier of Vishnu, to the Lord's supreme abode.
“O Rama, the fast day of Mohini Ekadashi removes the illusory attachments to material existence. There is no better fast day in all of the three worlds."
Lord Krishna concluded, "And so, Yudhisthira, there is no place of pilgrimage, no sacrifice, and no charity that can bestow merit equal to even one sixteenth of the merit a faithful devotee of Mine obtains by observing Mohini Ekadashi, and he who hears and studies the glories of Mohini Ekadashi achieves the merit of giving away one thousand cows in charity."
This year Mohini Ekadashi falls on May 15, 2019.