After the Samudra manthan, once Lord Vishnu went to the Patal Lok or the underworld. There He was infatuated by the beautiful women. Lord Vishnu had many sons during His stay there. But all His sons turned out to be cruel and monstrous. They started tormenting all Gods and humans alike. It was then Lord Shiva took the form of an ox or Rishabha and killed all the cruel sons of Lord Vishnu. Lord Vishnu came to fight the ox but after recognising that it was Lord Shiva’s incarnation, He returned to His abode.