Genesis 21:27-32

So the two of them made a covenant. Abraham took sheep and cattle and gave them to Abimelech. Abraham set aside seven sheep from his flock. Abimelech said, “What does this mean? These seven sheep you’ve set aside.” Abraham said, “It means that when you accept these seven sheep, you take it as proof that I dug this well, that it’s my well.” That’s how the place got named Beersheba (the Oath-Well), because the two of them swore a covenant oath there. After they had made the covenant at Beersheba, Abimelech and his commander, Phicol, left and went back to Philistine territory.