The Ekadashi that fall in Shukla paksha of Shravan month is called Pavitropana or Putrada Ekadashi . Whoever desires happiness in this world and the next should certainly fast from all grains and legumes on this holy day. Indeed, whoever simply hears the glories of Putrada Ekadashi becomes completely free of all sins, is blessed with a good son, and surely ascends to heaven after death.
Shri Yudhisthira Maharaja said, 'Oh Madhusudana, Oh killer of the Madhu demon, please be merciful to me and describe to me the Ekadashi that occurs during the light fortnight of the month of Shravana (July-August).' The Supreme Lord, Sri Krishna, replied, 'Yes, Oh king, I shall happily narrate its glories to you, for just by hearing about this sacred Ekadashi one attains the merit of performing a horse sacrifice.'
At the dawn of Dvapara-yuga there lived a king by the name of Mahijita, who ruled the kingdom of Mahismati-puri. Because he had no son, his entire kingdom seemed utterly cheerless to him. A married man who has no son gains no happiness in this life or the next.
For a long time this king tried very hard to obtain an heir, but to no avail. Seeing his years advancing ever onwards, King Mahijita became increasingly anxious. One day he told an assembly of his advisers: "I have committed no sin in this life, and there is no ill-gotten wealth in my treasury. I have never usurped the offerings to the demigods or Brahmans. When I waged war and conquered kingdoms, I followed the rules and regulations of the military art, and I have protected my subjects as if they were my own children. I punished even my own relatives if they broke the law, and if my enemy was gentle and religious I welcomed him. Oh twice-born souls, although I am a religious and faithful follower of the Vedik standards, still my home is without a son. Kindly tell me the reason for this."
Hearing this, the king's Brahman advisers discussed the subject among themselves, and with the aim of benefiting the king they visited the various ashrams of the great sages. At last they came upon a sage who was austere, pure, and self-satisfied, and who was strictly observing a vow of fasting. His senses were completely under control, he had conquered his anger, and he was expert at performing his occupational duty. Indeed, this great sage was expert in all the conclusions of the Vedas, and he had extended his life span to that of Lord Brahma himself. His name was Lomasa Rishi, and he knew part, present, and future. After each kalpa passed, one hair would fall out of his body. All the king's Brahman advisers very happily approached him one by one to offer their humble respects.
Captivated by this great soul, King Mahijita's advisers offered obeisance's to him and said very respectfully, Only because of our great good fortune, Oh sage, have we been allowed to see you.
Lomasa Rishi saw them bowing down to him and replied, "Kindly let me know why you have come here. Why are you praising me? I must do all I can to solve your problems, for sages like me have only one interest: to help others. Do not doubt this."
The king's representatives said, "We have come to you, Oh exalted sage, to ask for your help in solving a very serious problem. Oh sage, you are like Lord Brahma. Indeed, there is no better sage in the entire world. Our king, Mahijita, is without a son, though he has sustained and protected us as if we were his sons. Seeing him so unhappy on account of being sonless, we have become very sad, Oh sage, and therefore we have entered the forest to perform severe austerities. By our good fortune we happened upon you. Everyone's desires and activities become successful just by your darshana. Thus we humble ask that you tell us how our kind can obtain a son."
Hearing their sincere plea, Lomasa Rishi absorbed himself in deep meditation for a moment and at once understood the king's previous life. Then he said, "Your ruler was a merchant in his past life, and feeling his wealth insufficient, he committed sinful deeds. He traveled to many villages to trade his goods. Once, at noon on the day after the Ekadashi that comes during the light fortnight of the month of Jyeshtha , he became thirsty while traveling from place to place. He came upon a beautiful pond on the outskirts of a village, but just as he was about to drink at the pond a cow arrived there with her new-born calf. These two creatures were also very thirsty because of the heat, but when the cow and calf started to drink, the merchant rudely shoved them aside and selfishly slaked his own thirst. This offense against a cow and her calf has resulted in your king's being without a son now. But the good deeds he performed in his previous life have given him ruler ship over an undisturbed kingdom."
Hearing this, the king's advisers replied, "Oh renowned rishi, we have heard that the Vedas say one can nullify the effects of one's past sins by acquiring merit. Be so kind as to give us some instruction by which our king's sins can be destroyed; please give him your mercy so that a prince will take birth in his family."
Lomasa Rishi said, "There is an Ekadashi called Putrada, which comes during the light fortnight of the month of Shravan. On this day all of you, including your king, should fast and stay awake all night, strictly following the rules and regulations. Then you should give the king whatever merit you gain by this fast. If you follow these instructions of mine, he will surely be blessed with a fine son."
All the king's advisers became very pleased to hear these words from Lomasa Rishi, and they all offered him their grateful obeisance's. Then, their eyes bright with happiness, they returned home.
When the month of Shravan arrived, the king's advisers remembered the advice of Lomasa Rishi, and under their direction all the citizens of Mahismati-puri, as well as the king, fasted on Ekadashi. And on the next day, DvAdasi, the citizens dutifully offered their accrued merit to him. By the strength of all this merit, the queen became pregnant and eventually gave birth to a most beautiful son.
O Yudhisthira, Lord Krishna concluded, "The Ekadashi that comes during the light fortnight of the month of Shravan has thus rightfully become famous as Putrada . Whoever desires happiness in this world and the next should certainly fast from all grains and legumes on this holy day. Indeed, whoever simply hears the glories of Putrada Ekadashi becomes completely free of all sins, is blessed with a good son, and surely ascends to heaven after death."
Source : Bhavishya Purana