Story of Narasimha avatar of Vishnu and Demon Ambarya is mentioned in the Brahma Purana. This story happens after Narasimha vanquished Hiranyakashipu.
Legend has it that after killing Hiranyakashipu, Narasimha roamed around the world annihilating all that practiced Adharma. He killed scores of demons.
He then arrived on the banks of Godavari River near Dandakaranya forest.
Demon Ambarya ruled the region. Even Devas were unable to defeat him.
Demon Ambarya and his large army attacked Narasimha. In the terrible fight, the entire army was vanquished. The invincible demon was killed and the place was rid of his terror.
The place where the demon was vanquished came to be known as Narasimha tirtha