"One formulation of the doctrine is given in the religious poem the Bhagavad Gita when charioteer Lord Krishna tells Arjuna: “Whenever there is a decline of righteousness and rise of unrighteousness then I send forth Myself. For the protection of the good, for the destruction of the wicked, and for the establishment of righteousness, I come into being from age to age.”"
January 1, 1970
https://en.wikiquote.org/wiki/Incarnation