I Samuel 20:16-17, 42

So Jonathan made a covenant with the house of David, saying, “Let the LORD require it at the hand of David’s enemies.” Now Jonathan again caused David to vow, because he loved him; for he loved him as he loved his own soul.

Then Jonathan said to David, “Go in peace, since we have both sworn in the name of the LORD, saying, ‘May the LORD be between you and me, and between your descendants and my descendants, forever.’ ” So he arose and departed, and Jonathan went into the city.