Mbh 1.20.3

‘Sauti continued, ‘Thus wagering with each other about menial service as a slave, the sisters went home, and resolved to satisfy themselves by examining the horse next day. And Kadru, bent upon practising a deception, ordered her thousand sons to transform themselves into black hair and speedily cover the horse’s tail in order that she might not become a slave. But her sons, the snakes, refusing to do her bidding, she cursed them, saying, ‘During the snake-sacrifice of the wise king Janamejaya of the Pandava race, Agni shall consume you all.’ And the Grandsire (Brahman) himself heard this exceedingly cruel curse pronounced by Kadru, impelled by the fates. And seeing that the snakes had multiplied exceedingly, the Grandsire, moved by kind consideration for his creatures, sanctioned with all the gods this curse of Kadru. Indeed, as the snakes were of virulent poison, great prowess and excess of strength, and ever bent on biting other creatures, their mother’s conduct towards them--those persecutors of all creatures,--was very proper for the good of all creatures. Fate always inflicts punishment of death on those who seek the death of other creatures. The gods, having exchanged such sentiments with one another, supported Kadru’s action (and went away). And Brahman, calling Kasyapa to him, spake unto him these words, ‘O thou pure one who overcomest all enemies, these snakes begotten by you, who are of virulent poison and huge bodies, and ever intent on biting other creatures, have been cursed by their mother. O son, do not grieve for it in the least. The destruction of the snakes in the sacrifice hath, indeed, been ordained long ago’ Saying this, the divine Creator of the Universe comforted Kasyapa and imparted to that illustrious one the knowledge of neutralising poison.”