Indra, the king of the devas, was once driven out of devaloka by an asura named Vritra
the asura was the recipient of a boon whereby he could not be killed by any weapon that was known till the date of his receiving the boon Indra, who lost all hope of recovering his kingdom went to seek the aid of Vishnu. Vishnu revealed to Indra that only the weapon made from the bones of the sage Dadhichi would defeat Vritra.
To kill Asura Vritra All devs comes to sage Dadhichi to let his bones become that only weapon to kill demon. He acceded the request but said that he wished that he had time to go on a pilgrimage to all the holy rivers Indra then brought together all the waters of the holy rivers to Naimisaranya, thereby allowing the sage to have his wish fulfilled without a further loss of time. Namisharan temple is counted as one of the eight temples of Vishnu that self-manifested and is classified as Swayamvyakta Kshetra.
