1 Samuel 20:31-33

For as long as the son of Jesse lives on the earth, neither you [as heir to the throne] nor your kingdom will be established. So now, send [someone] and bring him to me, for he must die.” Jonathan answered Saul his father, “Why must he be put to death? What has he done?” Then Saul hurled his spear at him to strike him down, so Jonathan knew [without any doubt] that his father had decided to put David to death.