BG 4.7
यदा यदा हि धर्मस्य ग्लानिर्भवति भारत। अभ्युत्थानमधर्मस्य तदाऽऽत्मानं सृजाम्यहम्
yadā yadā hi dharmasya glānir bhavati bhārata abhyutthānam adharmasya tadātmānaṁ sṛijāmyaham
Whenever spirituality decays and materialism is rampant, then, O Arjuna, I reincarnate myself.
Translated by Shri Purohit Swami
Whenever there is a decline of righteousness and an increase of unrighteousness, O Arjuna, then I manifest Myself.
Translated by Swami Sivananda
Word meanings (from the gita/gita dataset)
yadā yadā—whenever; hi—certainly; dharmasya—of righteousness; glāniḥ—decline; bhavati—is; bhārata—Arjun, descendant of Bharat; abhyutthānam—increase; adharmasya—of unrighteousness; tadā—at that time; ātmānam—self; sṛijāmi—manifest; aham—I