Genesis 21:31-34

Therefore that place was called Beersheba, because there both of them swore an oath. So they made a covenant at Beersheba. Then Abimelech and Phicol the commander of his army rose up and returned to the land of the Philistines. Abraham planted a tamarisk tree in Beersheba and called there on the name of the LORD, the Everlasting God. And Abraham sojourned many days in the land of the Philistines.