Bereshis 27:39-40

And Yitzchak aviv answered and said unto him, Hinei, thy moshav (dwelling) shall be the fatness of ha'aretz, and of the tal HaShomayim from above; And by thy cherev shalt thou live, and shalt serve achicha; and it shall come to pass when thou shalt become restless, that thou shalt break his ol (yoke) from off thy tzavar (neck).