Vishnupurana 5.1.63

5.1.63

tataḥ kṣayamaśeṣāste daiteyā dharamītale /
prayāsyanti na saṃdeho maddṛpātavicūrṇitāḥ //

When Brahmá had ended, the supreme lord plucked off two hairs, one white and one black, and said to the gods, "These my hairs shall descend upon earth, and shall relieve her of the burden of her distress. Let all the gods also, in their own portions, go down to earth, and wage war with the haughty Asuras, who are there incorporate, and who shall every one of them be destroyed. Doubt not of this: they shall perish before the withering glance of mine eyes. This my (black) hair shall be impersonated in the eighth conception of the wife of Vasudeva, Devakí, who is like a goddess; and shall slay Kansa, who is the demon Kálanemi." Thus having spoken, Hari disappeared; and the gods bowing to him, though invisible, returned to the summit of mount Meru, from whence they descended upon earth.