When the cowherd men of Vṛndāvana, under instruction of Kṛṣṇa, stopped offering sacrifice to the heavenly King, Indra, the whole tract of land known as Vraja was threatened with being washed away by constant heavy rains for seven days. Lord Kṛṣṇa, out of His causeless mercy upon the inhabitants of Vraja, held up the hill known as Govardhana with one hand only, although He was only seven years old. He did this to protect the animals from the onslaught of water.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
गोपैर्मखे प्रतिहते व्रजविप्लवाय देवेऽभिवर्षति पशून् कृपया रिरक्षुः । धर्तोच्छिलीन्ध्रमिव सप्तदिनानि सप्त- वर्षो महीध्रमनघैककरे सलीलम्
gopairmakhe pratihate vrajaviplavāya deve'bhivarṣati paśūn kṛpayā rirakṣuḥ | dhartocchilīndhramiva saptadināni sapta- varṣo mahīdhramanaghaikakare salīlam
SB 2.7.32