BHAGAVAD GITA
Ch. 4, Verse 8
Krishna speaks:
परित्राणाय साधूनां विनाशाय च दुष्कृताम्। धर्मसंस्थापनार्थाय सम्भवामि युगे युगे॥
paritrāṇāya sādhūnāṁ vināśāya ca duṣkṛtām | dharma-saṁsthāpanārthāya sambhavāmi yuge yuge ||
To protect the righteous, to annihilate the wicked, and to reestablish the principles of dharma, I appear millennium after millennium.