Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 9
Sanskrit:
एतदर्थोऽवतारोऽयं भूभारहरणाय मे ।संरक्षणाय साधूनां कृतोऽन्येषां वधाय च ॥ ९ ॥
ITRANS:
etad-artho ’vatāro ’yaṁbhū-bhāra-haraṇāya mesaṁrakṣaṇāya sādhūnāṁkṛto ’nyeṣāṁ vadhāya ca
Translation:
This is the purpose of My present incarnation — to relieve the earth of its burden, protect the pious and kill the impious.