From the book Karma and Creativity:

This passage is from the Bradaranyaka Upanisad.

"Now as a caterpillar, when it has come to the end of a

blade of grass, in taking the next step draws itself together

towards it, just so this soul in taking the next step strikes

down this body, dispels its ignorance, and draws itself

together." 

In Hindu tradition, perhaps the earliest hint of the notion of rebirth is found here, contemporaneous with the rise of Buddhism.