The glories of Pavitra Ekadasi are described in the Bhavisyottara Purana in the conversation between Lord Krsna and Maharaja Yudhisthira.

Once Maharaja Yudhisthira asked Krsna, “O Madhusudana, the killer of the Madhu demon, what is the name and the glories of the Ekadasi that occurs during the waxing moon in the month of July/August? Please explain this to me in detail.”

Lord Krsna replied, “O King! The name of this sacred Ekadasi is Pavitra Ekadasi. Now please here attentively about the topics of this Ekadasi, which destroyes one’s sinful reactions. By hearing the glories of this Ekadasi, one obtains the result of performing a Vajapeya sacrifice. “Long ago in the beginning of Dvapara-yuga there was a King named Mahijit who ruled the kingdom named Mahismatipuri. The king had no sons and was unhappy while conducting his activities. A married man who has no son has no happiness either in this life or in the next. For many years the King tried to get a son, but he was not fortunate enough to get a jewel-like son who would give him all pleasure.

“One day, realizing his own pathetic situation, the King called his subjects whom he treated as his children to the royal assembly and said to them, ‘O dear subjects, I have never committed any sinful activity in my life, I did not increase my treasury by unlawfully earned wealth, I did not plunder the wealth of the brahmanas and the demigods, rather I have conquered this world by following the proper code of conduct, and I have maintained all of you like my own children, I have never hesitated to award due punishment even to my dear ones like my brother and relatives according to their faults, and I have shown due respect even to my enemy if he was gentle and pious. O brahmanas, in spite of traveling on the religious path like this, I am bereft of a son. Please consider carefully the reason behind this and advise me.’

“After hearing these lamenting words of King Mahijit, the King’s brahmana advisers discussed the subject matter among themselves and decided that for the benefit of the King they would go to the forest and visit the asramas of the great sages who know the past, present and future. After entering the forest and wandering here and there, they came across various asramas of great sages. Finally they met Lomasa Muni, who was engaged in severe austerities. His body was spiritual and full of bliss, and he strictly observed the vow of fasting. He was self-controlled and knew the science of eternal religious principles, and he was well convesant with the knowledge of the scriptures. His duration of life was as long as that of Brahma, and he was an effulgent saint. When a kalpa of Brahma passes, one hair (loma) falls from his body. That is why the name of the sage is Lomasa. The sage Lomasa was the knower of past, present and future. “Enchanted by this great sage, the advisors of the King offered their obeisances to him and spoke with humility. ‘O great sage! Due to our great fortune we have met a great should like you.’ The sage Lomasa inquired, ‘Who are you all? Why have you come here? Why are you praising me like this?’ The brahmanas replied, ‘O great sage! We have come to you to solve our dilemma. O Lord! Our king Mahijit, has no sons. We are his subjects, and the King treats us as his own children. We are feeling disturbed on seeing the distress of the King. O best of the brahamanas, we want to strictly undergo austerity here. It is the good fortune of the King that today we have met a great personality like you. By the darsana of a great personality, a man certainly attains all perfections. Please instruct us in such a way that our sonless king can have a son.’

“After hearing their sincere prayers, the sage Lomasa entered into a deep meditation for a moment and immediately understood the King Mahijit’s previous life. He then said that in his previous life this king was a poor vaisya, or merchant. He committed a sinful deed. Once while traveling from village to village in the course of his business he became overwhelmed with thirst. It was the midday of Dvadasi in the month of July. Soon he found a beautiful lake and decided to drink its water. At that time a cow and her newly born calf came there to drink water. As the cow began to drink water from the lake the merchant immediately drove her away and began to drink water himself. As a result of obstructing the thirsty cow from drinking water, the merchant had committed a sin. For this reason, though the merchant has now been born as King Mahijit, by the influence of his piety he cannot get a son.

“On hearing these words of the great sage, the King’s advisors said, ‘O great sage! It is stated in the Puranas that by the influence of piety all one’s sinful reactions are counteracted. Therefore please instruct us in such a way that all the sinful reactions of the King will be destroyed and he can obtain a son.’

“The great sage Lomasa replied, ‘There is a famous auspicious Ekadasi known as Pavitra Ekadasi which occurs during the waxing moon in the month of July/August. You and your King should properly observe this Ekadasi. Thereafter you should give the piety that you earn by observing this Ekadasi to your King. If you follow my instruction, then the King will certainly be blessed with a son. After hearing these words from Sage Lomasa, all the King’s advisors became happy and satisfied. They offered their obeisances to the sage and returned home. Then they met King Mahijit and explained to him in detail what they had heard from the great Sage Lomasa.

“Thereafter, when the proper time arrived, the King’s advisors remembered the advice of the sage and properly observed the vow of Pavitra Ekadasi with the King. On the day of Dvadasi they gave away their accumulated piety to the King as advised by the sage. By the influence of this piety the Queen became pregnant and in due course of time she gave birth to a beautiful son.

“O King Yudhisthira! Anyone who observes this sacred Ekadasi is relieved from sinful reactions and becomes happy both in this life and in the next. One who hears the glories of this Ekadasi obtains the happiness derived from having a son in this life and goes back to Godhead in his next life.”