Mahabharata 12.335.63

12.335.63

nirīkṣya cāsurendrau tau tato yuddhe mano dadhe |
atha yuddhaṃ samabhavattayornārāyaṇasya ca || 63 ||

Thereupon an encounter took place between those two on one side and Narayana on the other. The Asuras Madhu and Kaitabha were embodiments of the attributes of Rajas and Tamas. Narayana slew them both for gratifying Brahma. He thence came to be called by the name of Madhusudana (slayer of Madhu). Having compassed the destruction of the two Asuras and restored the Vedas to Brahma, the Supreme Being dispelled the grief of Brahma. Aided then by Hari and assisted by the Vedas, Brahma created all the worlds with their mobile and immobile creatures. After this, Hari, granting unto the Grandsire intelligence of the foremost order relating to the Creation, disappeared there and then for going to the place he had come from. It was thus that Narayana, having assumed the form equipt with the horse-head, slew the two Danavas Madhu and Kaitabha (and disappeared from the sight of Brahma). Once more, however, he assumed the same form for the sake of causing the religion of Pravritti to flow in the universe.'