Genesis 21:31-34

So that place was called Beersheba, because the two men swore an oath there. After the treaty had been made at Beersheba, Abimelek and Phicol the commander of his forces returned to the land of the Philistines. Abraham planted a tamarisk tree in Beersheba, and there he called on the name of the LORD, the Eternal God. And Abraham stayed in the land of the Philistines for a long time.