4:8  

परित्राणाय साधूनां विनाशाय च दुष्कृताम् ।
धर्मसंस्थापनार्थाय सम्भवामि युगे युगे ॥४-८॥

paritraaNaaya saadhoonaaM winaashaaya cha duShkRRitaam ।

dharmasaMsthaapanaarthaaya sambhawaami yuge yuge ॥४-८॥

Source: Automatic ITRANS Transliteration

For the protection of the righteous, for the destruction of evil-doers,
For the establishment of integrity, I manifest in age after age.

Source: Milind S. Pandit

Source: The Bhagavad-Gita: The Sacred Song

In order to deliver the pious and to annihilate the miscreants, as well as to reestablish the principles of religion, I advent Myself millennium after millennium.

Source: Bhagavad Gita As It Is