Bhagavad Gita 4.8
परित्राणाय साधूनां विनाशाय च दुष्कृताम्। धर्मसंस्थापनार्थाय सम्भवामि युगे युगे।।4.8।।
paritrāṇāya sādhūnāṃ vināśāya ca duṣkṛtām| dharmasaṃsthāpanārthāya sambhavāmi yuge yuge||4.8||
paritranaya sadhunam vinashaya ca dushkritam dharmasamsthapanarthaya sambhavami yuge yuge4.8
Meaning
For the protection of the good, the destruction of the wicked, and the establishment of dharma, Krishna incarnates age after age. This is His eternal promise to humanity.
साधु पुरुषों के रक्षण, दुष्कृत्य करने वालों के नाश, तथा धर्म संस्थापना के लिये, मैं प्रत्येक युग में प्रगट होता हूँ।
This is verse 8 of 42 in Chapter 4 (Jnana Karma Sanyasa Yoga) of the Bhagavad Gita.