Adi Parva - Astika Parva 26

"Sauti said, 'Hearing the respective speeches of all the snakes, and hearing also the words of Vasuki, Elapatra began to address them, saying, 'That sacrifice is not one that can be prevented. Nor is king Janamejaya of the Pandava race from whom this fear proceedeth, such that he can be hindered. The person, O king, who is afflicted by fate hath recourse to fate alone; nothing else can be his refuge. Ye best of snakes, this fear of ours hath fate for its root. Fate alone must be our refuge in this. Listen to what I say. When that curse was uttered, ye best of snakes, in fear I lay crouching on the lap of our mother. Ye best of snakes, and O lord (Vasuki) of great splendour, from that place I heard the words the sorrowing gods spake unto the Grandsire. The gods said, 'O Grandsire, thou god of gods who else than the cruel Kadru could thus, after getting such dear children, curse them so, even in thy presence? And, O Grandsire, by thee also hath been spoken, with reference to those words of hers, 'Be it so.' We wish to know the reason why thou didst not prevent her.' Brahman replied, 'The snakes have multiplied. They are cruel, terrible in form and highly poisonous. From desire of the good of my creatures, I did not prevent Kadru then. Those poisonous serpents and others who are sinful, biting others for no faults, shall, indeed, be destroyed, but not they who are harmless and virtuous. And hear also, how, when the hour comes, the snakes may escape this dreadful calamity.
There shall be born in the race of the Yayavaras a great Rishi known by the name of Jaratkaru, intelligent, with passions under complete control.

That Jaratkaru shall have a son of the name of Astika. He shall put a stop to that sacrifice. And those snakes who shall be virtuous shall escape therefrom. The gods said, 'O thou truth-knowing one, on whom will Jaratkaru, that foremost Muni, gifted with great energy and asceticism, beget that illustrious son?' Brahma answered, 'Gifted with great energy, that best Brahmana shall beget a son possessed of great energy on a wife of the same name as his. Vasuki, the king of the snakes, hath a sister of the name of Jaratkaru; the son, of whom I speak, shall be born of her,
and he shall liberate the snakes.'

"Elapatra continued, 'The gods then said unto the Grandsire, 'Be it so.' And the lord Brahman, having said so unto the gods, went to heaven. O Vasuki, I see before me that sister of thine known by the name of Jaratkaru. For relieving us from fear, give her as alms unto him (i.e., the Rishi), Jaratkaru, of excellent vows, who shall roam abegging for a bride. This means of release hath been heard of by me!'"