2 Samuel 1:15

He smote him that he died Abarbinel thinks that, as the man was an Amalekite, David supposed that he had killed Saul out of revenge for the slaughter he had made of the Amalekites. But, if not; if the fact were as this Amalekite stated, and Saul bid him despatch him, “David rightly judged, that Saul had no power over his own life; and, consequently, should not have been obeyed in such a command: God and the state had as much right to his life when he was weary of it as when he most loved it. And, besides all this, it behooved David to vindicate his own innocence to the world, by so public an execution: he might otherwise, perhaps, have been branded with the guilt of employing that wretch to murder his persecutor. David also, doubtless, had it in view to deter others by this example. He consulted his own safety in this, as Cesar is said, by restoring the statues of Pompey, to have fixed his own. This was a wise lecture to princes, and many of them have unquestionably profited by it.” Delaney.