Genesis 21:31-34

Then he named the place Beersheba (which means “well of the oath”), because that was where they had sworn the oath. After making their covenant at Beersheba, Abimelech left with Phicol, the commander of his army, and they returned home to the land of the Philistines. Then Abraham planted a tamarisk tree at Beersheba, and there he worshiped the LORD, the Eternal God. And Abraham lived as a foreigner in Philistine country for a long time.