Midrasch zu Bereschit 31:46

Jacob made a covenant with the people of the land, because Laban said to him: I know that the Holy One, blessed be He, will give to thy seed in the future all these lands; make a covenant of an oath with me, that the Israelites will not take possession of the land of Edom. He made with him a covenant with an oath, as it is said, "And Jacob said unto his brethren, Gather ye stones" (Gen. 31:46). Were they his brethren? Were they not his sons? But this teaches thee that a man's sons are like his brethren. Laban said to him: If the Israelites obtain possession of the land (of Canaan), then they must not come into the land of Edom for an evil purpose, and if Edom obtain possession they must not come into the land of Israel for evil, as it is said, "That I will not pass over this heap to thee, and that thou shalt not pass over this heap and this pillar unto me, for harm" (Gen. 31:52).