The earring in Vishnu's well

Before the city had a name, Vishnu came to the riverbank and cut a pool out of the ground with the edge of his discus. He sat beside it and did not move for fifty thousand years, and the sweat of that effort filled the pool. Shiva came with Parvati to look at what his friend had done, and the sight pleased him so much that he shook, and a jewel dropped from his ear into the water. Because of the jewel the pool is Manikarnika, the ear-ornament, and because Shiva was pleased he promised that anyone who died there would not be born again. The burning-ground beside the pool has never been cold since. Another telling says it was Parvati's earring that fell and that Shiva promised to search for it there for ever, which is why he never leaves Kashi. Kashi's three great claims, the pillar of light, this pool and the tirtha where Bhairava's skull fell away, all rest on the Kashi Khanda.