After winning the war, the Pandavas went on a pilgrimage to Mount Kailash. They wanted Shiva to cleanse them of the sin of killing so many people. When Shiva saw them he hid. When they couldn't find him, Yudhisthira said, "I know you have hidden because we have sinned, but we will not leave without seeing you." As they moved ahead, a bull attacked them. Bhima started fighting it.Bhima fighting with the bull The bull hid his head within a crack in a rock. Bhima tried to pull him out by his tail, but the body of the bull got separated from his head. The body turned into a Shivalinga from which Shiva appeared and forgave them their sins.
The linga is still present in the Himalayas and is called Kedarnath
source : kidagen