From The Jātakas: Birth Stories of the Bodhisatta
[herein paraphrased]
Once while residing in Jetavana Grove, the Teacher told this story on observing the precepts of uposatha.
Once the king of Magadha, at constant war with the king of Anga, obtaining the help of the Naga king who dwelt in the river Campa, defeated his rival. Thereafter he held an annual festival in honour of the Naga king.
The Bodhisatta, a very poor man, saw Campeyyas splendor on his way to the feast and longed for a like greatness. As a result, after death, he was born in the Naga world where he became king under the name of Campeyya.
Realizing what had happened, he felt disgust at his position as a Naga and made many attempts to observe religious vows, hoping, in this way, to gain release. But he was foiled in his efforts by his consort Sumana.
At last he came to the world of men, where he kept fast on uposatha days, lying on an ant hill. There he was taken captive by a snake charmer who tortured him in various ways and took him about, exhibiting him for gain. By certain tokens of which Campeyya had earlier warned her, Sumana knew that her husband had been taken captive and, after much searching, she discovered him just as the snake charmer was about to give a performance before Uggasena, king of Benares.
The whole story was then revealed, and the snake charmer set Campeyya free, on the command of Uggasena. That Uggasena might be convinced of the truth of the story, he was invited to the Naga world, where he and his retinue were lavishly entertained.
”You, who have acquired magical powers and great potency, have all the pleasures of the senses at your disposal. Nāga king, why do you proclaim the human realm better than this?”
”Nowhere but in the realm of humans is there purity and self-control. Having attained human birth I will make an end death and rebirth.”
The story was related by the Teacher in connection with the observance of uposatha vows.
“In this way the wise abandoned the nāga realm and kept the uposatha. Devadatta was the snake charmer and Sariputta was Uggasena. Rahulamata was Sumana. I was the nāga king, Campeyya.”
Glossary:
nāga: legendary beings, part snake and part human, endowed with supernatural powers.
uposatha: day of purification and observation of the precepts, falling on day of new moon, full moon, and quarter moon.