Adi Parva - Astika Parva 27

"Sauti said, 'O best of regenerate ones, hearing these words of Elapatra,
all the serpents, in great delight, exclaimed, 'Well said, well said!'
And from that time Vasuki set about carefully bringing up that maiden,
viz., his sister Jaratkaru. And he took great delight in rearing her.

"And much time did not elapse from this, when the gods and the Asuras,
assembling together, churned the abode of Varuna. And Vasuki, the
foremost of all gifted with strength, became the churning-cord. And
directly the work was over, the king of the snakes presented himself
before the Grandsire. And the gods, accompanied by Vasuki, addressed the
Grandsire, saying, 'O lord, Vasuki is suffering great affliction from
fear of (his mother's curse). It behoveth thee to root out the sorrow,
begotten of the curse of his mother, that hath pierced the heart of
Vasuki desirous of the weal of his race. The king of the snakes is ever
our friend and benefactor. O Lord of the gods, be gracious unto him and
assuage his mind's fever.'

"Brahman replied, 'O ye immortals, I have thought, in my mind, of what ye
have said. Let the king of the snakes do that which hath been
communicated to him before by Elapatra. The time hath arrived. Those only
shall be destroyed that are wicked, not those that are virtuous.
Jaratkaru hath been born, and that Brahmana is engaged in hard ascetic
penances. Let Vasuki, at the proper time, bestow on him his sister. Ye
gods, what hath been spoken by the snake Elapatra for the weal of the
snakes is true and not otherwise.'

"Sauti continued, 'Then the king of the snakes, Vasuki, afflicted with
the curse of his mother, hearing these words of the Grandsire, and
intending to bestow his sister of the Rishi Jaratkaru, commanded all the
serpents, a large numbers of whom were ever attentive to their duties, to
watch the Rishi Jaratkaru, saying, 'When the lord Jaratkaru will ask for
a wife, come immediately and inform me of it. The weal of our race
depends upon it.'"