The greatness of Kaisika Ekadasi is found in the Kaisika Puranam which is part of the Varaha Purana.
Nampaduvan was born in a Chandala family, a low class family. But he was an ardent devotee of Vishnu. He used to daily sing praise of Vishnu in a temple. Once on Kartik Shukla Ekadasi, while he was going for his daily prayer, he was stopped by a Brahma Rakshas (fierce ghostly form). The Rakshas had not eaten food for several days.
The Rakshas wanted to eat Nampaduvan immediately. Nampaduvan was ready to offer himself as food but he wanted to complete the day’s prayer before Vishnu.
Initially hesitant, the Rakshas agreed to Nampaduvan.
Nampaduvan then went to the temple and offered his prayers. He sang glory of Bhagvan Srihari Vishnu in the Kaisika Tune.
After completing his prayers, Nampaduvan started walking towards the Brahma Rakshas. Suddenly an old man appeared there and advised Nampaduvan to escape in another route. But Nampaduvan was not ready to do that. The old man was Vishnu himself.
Nampaduvan went and offered himself to the Rakshas. But his hunger had vanished and instead he was moved by the truthfulness of the Vishnu devotee.
The Brahma Rakshas then told his story – he was a Brahmin who was cursed to become a Brahma Rakshas by his elders as he had not performed yajnas carefully.
The Rakshas then asked Nampaduvan to give the reward of one of his prayers so that he can get liberation.
But Nampaduvan told the Rakshas that he never sang for any reward – he always sang out of devotion and never bothered about its fruits.
Brahma Rakshas was dejected as he had to continue living in this weird and fierce form.
Nampaduvan then freely and wholeheartedly offered the fruit of the last song that he had sung in praise of Vishnu to the Brahma Rakshas.
No sooner had he spoken, the Rakshas was transformed into his Brahmin form and was escorted to heaven.
This incident once again proved that birth is no criterion in Sanatana Dharma. Devotion to lord, adherence to Dharma and readiness to renounce the world are the important criteria.
It is believed that listening to the story will help in redemption of sins.