2 Samuel 1:12-16

They mourned and cried and fasted until the evening for Saul and his son Jonathan, and for the army of the Lord, the Israelites, that had been killed by the sword.

David asked man who brought him the report, “Where are you from?” “I'm the son of a foreigner,” he replied “I'm an Amalekite.”

“Why weren't you worried about killing the Lord's anointed one?” David asked.

David called over one of his men and said, “Go ahead, kill him!” So the man cut the Amalekite down and killed him.

David had told the Amalekite, “Your death is your own fault because you testified against yourself when you said, ‘I killed the Lord's anointed one.’”