Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 6

Sanskrit:

तं चण्डवेगविषवीर्यमवेक्ष्य तेनदुष्टां नदीं च खलसंयमनावतार: ।कृष्ण: कदम्बमधिरुह्य ततोऽतितुङ्ग-मास्फोट्य गाढरशनो न्यपतद् विषोदे ॥ ६ ॥

ITRANS:

taṁ caṇḍa-vega-viṣa-vīryam avekṣya tenaduṣṭāṁ nadīṁ ca khala-saṁyamanāvatāraḥkṛṣṇaḥ kadambam adhiruhya tato ’ti-tuṅgamāsphoṭya gāḍha-raśano nyapatad viṣode

Translation:

Lord Kṛṣṇa saw how the Kāliya serpent had polluted the Yamunā River with his terribly powerful poison. Since Kṛṣṇa had descended from the spiritual world specifically to subdue envious demons, the Lord immediately climbed to the top of a very high kadamba tree and prepared Himself for battle. He tightened His belt, slapped His arms and then jumped into the poisonous water.

Purport:

According to the ācāryas, Lord Kṛṣṇa also tied back the locks of His hair as He prepared to do battle with Kāliya.