I Samuel 20:14-17

And you shall not only show me the kindness of the LORD while I still live, that I may not die; but you shall not cut off your kindness from my house forever, no, not when the LORD has cut off every one of the enemies of David from the face of the earth.” 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.