“Sauti continued, ‘O son of Bhrigu! Vishnu with Brahman assented to it. And the lotus-eyed one (Vishnu) laid the hard task on the mighty Ananta, the prince of snakes. The powerful Ananta, directed thereto both by Brahman and Narayana, O Brahmana, tore up the mountain with the woods thereon and with the denizens of those woods. And the gods came to the shore of the Ocean with Ananta and addressed the Ocean, saying, ‘O Ocean; we have come to churn thy water for obtaining nectar.’
In plain words: Vishnu and Brahma agreed and gave the job to Ananta, the mighty king of snakes. Ananta tore up the whole mountain with its forests and animals. The gods carried it to the shore and told the Ocean they had come to churn it for nectar.