Genesis 21:27-31

27So Abraham brought sheep and cattle and gave them to Abimelek, and the two men made a treaty. 28Abraham set apart seven ewe lambs from the flock,

29and Abimelek asked Abraham, “What is the meaning of these seven ewe lambs you have set apart by themselves?”

30He replied, “Accept these seven lambs from my hand as a witness that I dug this well.”

31So that place was called Beersheba, Beersheba can mean well of seven and well of the oath. because the two men swore an oath there.