Mbh 12.209.2a

"'Bhishma said, "Formerly, on one occasion, while out ahunting, I arrived at the hermitage of Markandeya. There I beheld diverse classes of ascetics seated by thousands. The Rishis honoured me by the offer of honey and curds. Accepting their worship, I reverentially saluted them in return. The following that I shall recite was narrated there by the great Rishi Kasyapa. Listen with close attention to that excellent and charming account. In former days, the principal Danavas, endued with wrath and cupidity, and mighty Asuras numbering by hundreds and drunk with might, and innumerable other Danavas that were invincible in battle, became exceedingly jealous of the unrivalled prosperity of the gods. Oppressed (at last) by the Danavas, the gods and the celestial Rishis, failing to obtain peace, fled away in all directions. The denizens of heaven saw the earth looking like one sunk in sore distress. Overspread with mighty Danavas of terrible mien, the earth seemed to be oppressed with a heavy weight. Cheerless and grief-stricken, she seemed as if going down into the nether depths. The Adityas, struck with fear, repaired to Brahman, and addressing him, said, 'How, O Brahman, shall we continue to bear these oppressions of the Danavas?' The Self-born answered them, saying, 'I have already ordained what is to be done in this matter. Endued with boons, and possessed of might, and swelling with pride, those senseless wretches do not know that Vishnu of invisible form, that God incapable of being vanquished by the very deities all acting together, hath assumed the form of a boar. That Supreme Deity, rushing to the spot whither those wretches among Danavas, of terrible aspect, are dwelling in thousands below the earth, will slay them all.' Hearing these words of the Grandsire, foremost ones among the deities felt great joy. Sometime after, Vishnu, of mighty energy, encased in the form of a Boar, penetrating into the nether regions, rushed against those offspring of Diti.