1 Samuel 20:16-18

So Jonathan made a covenant with the house of David. [He added,] “May the LORD require it at the hands of David’s enemies. [that is, hold them accountable for any harm they inflict on David].” Jonathan made David vow again because of his love for him, for Jonathan loved him as himself. Then Jonathan said to David, “Tomorrow is the New Moon [festival], and you will be missed because your seat will be empty.