1 Samuel 20:5-8, 9, 33

David said, “Tomorrow marks the New Moon. I’m scheduled to eat dinner with the king. Instead, I’ll go hide in the field until the evening of the third. If your father misses me, say, ‘David asked if he could run down to Bethlehem, his hometown, for an anniversary reunion, and worship with his family.’ If he says, ‘Good!’ then I’m safe. But if he gets angry, you’ll know for sure that he’s made up his mind to kill me. Oh, stick with me in this. You’ve entered into a covenant of GOD with me, remember! If I’m in the wrong, go ahead and kill me yourself. Why bother giving me up to your father?”

“Never!” exclaimed Jonathan. “I’d never do that! If I get the slightest hint that my father is fixated on killing you, I’ll tell you.”

Saul threw his spear at him to kill him. That convinced Jonathan that his father was fixated on killing David.