It is an age-old practice for Indians to observe a fast (vrat) on Ekadasi days. According to Hindu calendar, Ekadasi occurs twice in the month. Ekadashi occurs twice in a month, once it occurs after 11 days from the full moon day and secondly 11 days from the new moon.
According to Hindu epic, Padma Purana, that describes the mythological relevance of Ekadasi.
There was a renowned sage, Jaimini Rishi, once asked the significance of Ekadashi from the great sage, Vyas.
Vyas explained that initially when the world was manifested, Lord Vishnu created a demonic creature known as (Papa-Purush) that was the embodiment of all types of sins. Subsequently, he created Yamaraj, so that anyone who sinned (signs of Papa-Purusha in him) would be punished and sent to Yamalok.
On a visit to Yamlok(the palace of Yam), Lord Vishnu noticed the sufferings of the people living there and had sympathy for them. He created goddess Ekadasi from his female powerand decided that anyone undertaking the Ekadasi fast would be absolved of his sins.