This incident took place when Shri Krishna went to Kailasha on the request of Devi Rukmini for a son.
When Shri Krishna reached Kailasha, he came across Ghantakarna. Ghantakarna is a follower of Rudra's friend Kubera. Ghantakarna was a Vishnu Dveshi who tied bells to his ears so that he won't be able to hear the names of Shri Narayana. He once pleased Shiva and the latter offered him to wish for a boon. Ghantakarna wished for Moksha and asked for it. Shiva then enlightened Ghantakarna by saying that Keshava alone can grant Moksha. Hearing this Ghantakarna started developing devotion towards Narayana. When he recognised Shri Krishna as Vishnu himself, he started hymning Narayana and decided to offer him something. He being a pisacha then immediately killed a brahmana and offered his body to Keshava. Shri Krishna then made him understand that killing brahmanas is a sin. Seeing Ghantakarna’s devotion, Keshava was very much pleased and touched his body with his hands. He gave up his pisach roop and assumed a form as handsome as cupid. He also got rid of Brahmahatya as well. Ghantakarna then got liberated thanks to the mercy of Keshava. And the brahmana who was killed is also restored to life by Shri Krishna.
