Mahabharata 9.36.35

9.36.35

yatra bhūyo nivavṛte prāṅmukhā vai sarasvatī |
ṛṣīṇāṃ naimiṣeyāṇāmavekṣārthaṃ mahātmanām || 35 ||

Swarming with numerous snakes, O monarch, it was the abode of Vasuki of great splendour, the king of the snakes. There 14,000 Rishis also had their permanent home. The celestials, having come there (in days of yore), had according to due rites, installed the excellent snake Vasuki as king of all the snakes. There is no fear of snakes in that place, O thou of Kuru's race! Duly giving away many valuables there unto the Brahmanas, Baladeva then set out with face towards the east and reached, one after another, hundreds and thousands of famous tirthas that occurred at every step. Bathing in all those tirthas, and observing fasts and other vows as directed by the Rishis, and giving away wealth in profusion, and saluting all the ascetics who had taken up their residence there, Baladeva once more set out, along the way that those ascetics pointed out to him, for reaching that spot where the Sarasvati turns in an eastward direction, like torrents of rain bent by the action of the wind. The river took that course for beholding the high-souled Rishis dwelling in the forest of Naimisha. Always smeared with white sandalpaste, Vala, having the plough for his weapon, beholding that foremost of rivers change her course, became, O king, filled with wonder."