Genesis 21:27-31

So Abraham took sheep and oxen and gave them to Abimelech, and the two of them made a covenant. And Abraham set seven ewe lambs of the flock by themselves. Then Abimelech asked Abraham, “What is the meaning of these seven ewe lambs which you have set by themselves?” And he said, “You will take these seven ewe lambs from my hand, that they may be my witness that I have dug this well.” Therefore he called that place Beersheba, because the two of them swore an oath there.