There was once a king of Ayodhya called Ambarisa. He was preparing for the grand yagna when Indra stole the sacrificial horse. The king wandered into the forest looking for another victim for the sacrifice when he found himself in the hermitage of a poor Brahmin called Rcika. Rcika had three sons and agreed to give one of them to the king for his sacrifice. But he is reluctant to part with the eldest son and his wife refuses to let the youngest one go, so the middle child Sunahshepa steps up and says that since his parents have not shown any interest in his life, he is available to the king.
On the way back, the king halts at Vishwamitra’s ashram. Tired, thirsty and extremely dejected, the boy hides himself in Vishwamitra’s lap and tells him his entire story. The sage agrees to help, but his four sons refuse to take the place of the boy. He curses them to be reborn as low caste humans and teaches the boy two hymns—one to Indra and another to Vishnu.
and Sunahshepa make their way back to the kingdom. The sacrifice is all arranged for and when the time comes, the boy recites the hymns just as he had been taught by Vishwamitra. Indra appears before him and frees him from the altar and the boy grew up to be a revered sage.
Story collected by: Arundhuti Dasgupta
Source: (Primary) Bala Kanda, Valmiki Ramayana, (Secondary) Rama and the Bards by R Antoine
Image: A 16th century Mughal era depcition of Ambarisha offering Sunahsepha in sacrifice