Pavitra Ekadasi is observed on the 11th day of the Shukla Paksha (waxing phase of moon) in the Shravan month as per traditional North Indian Calendar. The corresponding Ekadasi in other regions is known as Putrada Ekadashi. The Pavithra Ekadasi Vrat Katha (Story) narrates how a king was able to beget children after observing the Ekadasi.
Legend has it that a king named Mahijit had no children. The sad king one day convened the assembly of all the citizens and wanted to know what sin he had committed for not having children.
A group of citizens decided to visit the Ashramas of great saints and find out the reason why King Mahijit was not having children. After traveling for days they finally reached the Ashram of Sage Lomasa.
Sage Lomasa had the power to see the past, present and future. Sage Lomasa realized that King Mahijit was a merchant in his last birth and used to travel around selling his goods. Once during his journey he became very thirsty and soon reached a lake but he saw a thirsty cow drinking water and drove the cow away and drank water. The merchant had committed the sin of obstructing a thirsty cow from drinking water. It was due to this act that he was not having children in this birth.
Sage Lomasa advised them to ask the king to observe Pavitra Ekadasi so that all the sins will be erased. The king and the queen observed the Ekadasi and they soon had children.