Genesis 21 31
That's why he called the place Beersheba, because the two of them swore and oath to each other.
Compare with other 3 random translations
KJV Genesis 21:31Wherefore he called that place Beer-sheba; because there they sware both of them.
NCV Genesis 21:31So that place was called Beersheba because they made a promise to each other there.
AMP Genesis 21:31Therefore that place was called Beersheba [well of the oath], because there both parties swore an oath.