Vishnupurana 1.9.88

1.9.88

upary ākrāntavāñ chailaṃ bṛhadrūpeṇa keśavaḥ
tathāpareṇa maitreya yan na dṛṣṭaṃ surāsuraiḥ //

Being thus instructed by the god of gods, the divinities entered into alliance with the demons, and they jointly undertook the acquirement of the beverage of immortality. They collected various kinds of medicinal herbs, and cast them into the sea of milk, the waters of which were radiant as the thin and shining clouds of autumn. They then took the mountain Mandara for the staff; the serpent Vásuki for the cord; and commenced to churn the ocean for the Amrita. The assembled gods were stationed by Krishńa at the tail of the serpent; the Daityas and Dánavas at its head and neck. Scorched by the flames emitted from his inflated hood, the demons were shorn of their glory; whilst the clouds driven towards his tail by the breath of his mouth, refreshed the gods with revivifying showers. In the midst of the milky sea, Hari himself, in the form of a tortoise, served as a pivot for the mountain, as it was whirled around. The holder of the mace and discus was present in other forms amongst the gods and demons, and assisted to drag the monarch of the serpent race: and in another vast body he sat upon the summit of the mountain. With one portion of his energy, unseen by gods or demons, he sustained the serpent king; and with another, infused vigour into the gods.