2 Samuel 1:11 (KJV)

And the young man that told him said, As I happened by chance upon mount Gilboa, behold, Saul leaned upon his spear; and, lo, the chariots and horsemen followed hard after him.

And when he looked behind him, he saw me, and called unto me. And I answered, Here am I.

And he said unto me, Who art thou? And I answered him, I am an Amalekite.

He said unto me again, Stand, I pray thee, upon me, and slay me: for anguish is come upon me, because my life is yet whole in me.

So I stood upon him, and slew him, because I was sure that he could not live after that he was fallen: and I took the crown that was upon his head, and the bracelet that was on his arm, and have brought them hither unto my lord.

And they mourned, and wept, and fasted until even, for Saul, and for Jonathan his son, and for the people of the LORD, and for the house of Israel; because they were fallen by the sword.

And David said unto the young man that told him, Whence art thou? And he answered, I am the son of a stranger, an Amalekite.

And David said unto him, How wast thou not afraid to stretch forth thine hand to destroy the LORD's anointed?

And David called one of the young men, and said, Go near, and fall upon him. And he smote him that he died.

And David said unto him, Thy blood be upon thy head; for thy mouth hath testified against thee, saying, I have slain the LORD's anointed.