1 Samuel 20:11-17

“Let's go out to this field, and I'll tell you,” Jonathan answered. When they got there, Jonathan said: I swear by the LORD God of Israel, that two days from now I'll know what my father is planning. Of course I'll let you know if he's friendly toward you. But if he wants to harm you, I promise to tell you and help you escape. And I ask the LORD to punish me severely if I don't keep my promise. I pray that the LORD will bless you, just as he used to bless my father. Someday the LORD will wipe out all of your enemies. Then if I'm still alive, please be as kind to me as the LORD has been. But if I'm dead, be kind to my family. Jonathan and David made an agreement that even David's descendants would have to keep. Then Jonathan said, “I pray that the LORD will take revenge on your descendants if they break our promise.” Jonathan thought as much of David as he did of himself, so he asked David to promise once more that he would be a loyal friend.