Then also when the cowherd boys and their animals drank the poisoned water of the river Yamunā, and after the Lord [in His childhood] revived them by His merciful glance, just to purify the water of the river Yamunā He jumped into it as if playing and chastised the venomous Kāliya snake, which was lurking there, its tongue emitting waves of poison. Who can perform such herculean tasks but the Supreme Lord?
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
यद्वै व्रजे व्रजपशून् विषतोयपीथान् पालांस्त्वजीवयदनुग्रहदृष्टिवृष्ट्या । तच्छुद्धयेऽतिविषवीर्यविलोलजिह्व- मुच्चाटयिष्यदुरगं विहरन् ह्रदिन्याम्
yadvai vraje vrajapaśūn viṣatoyapīthān pālāṃstvajīvayadanugrahadṛṣṭivṛṣṭyā | tacchuddhaye'tiviṣavīryavilolajihva- muccāṭayiṣyaduragaṃ viharan hradinyām
SB 2.7.28