The prince, a son of the ruler of Sistan, enters the service of a snake, from a Tuti-nama (Tales of a Parrot): Thirty-seventh Night

A black snake rises from a hole to greet the prince of Sistan, in southeastern Iran. The prince, who had been wandering destitute through the wilderness has made a vow to serve the next living creature he meets. Although the snake is initially skeptical, he agrees to the arrangement and the prince is ultimately rewarded for his loyalty.