1 Samuel 26:6-9

6Then David said to Ahimelech the Hittite and to Abishai the son of Zeruiah, brother of Joab, “Who will go down with me to Saul in the camp?” And Abishai said, “I will go down with you.”

7So David and Abishai went to the army during the night, and there was Saul lying asleep inside the circle of the camp with his spear stuck in the ground by his head; and Abner and the people were lying around him.

8Then Abishai said to David, “God has given your enemy into your hand this day; now then, please let me strike him with the spear driving it to the ground with one stroke, and I will not strike him the second time.”

9But David said to Abishai, “Do not kill him, for who can put out his hand against the Lord’s anointed [king] and be guiltless (innocent)?”