Genesis 21:27-31

So Abraham took sheep and oxen and gave them to Abimelech, and the two men made a covenant. Abraham set seven ewe lambs of the flock apart. And Abimelech said to Abraham, “What is the meaning of these seven ewe lambs that you have set apart?” He said, “These seven ewe lambs you will take from my hand, that this may be a witness for me that I dug this well.” Therefore that place was called Beersheba, because there both of them swore an oath.