1 Samuel 26:6-9

6And David spake and said to Ahimelech the Hittite, and to Abishai the son of Zeruiah, Joab's brother, saying, Who will go down with me to Saul to the camp? And Abishai said, I will go down with thee.

7And David and Abishai came to the people by night, and behold, Saul lay sleeping within the wagon-defence, and his spear stuck in the ground at his head; and Abner and the people lay round about him.

8And Abishai said to David, 1God has delivered thine enemy into thy hand this day; and now let me smite him, I pray thee, with the spear, even to the ground once, and I will not do it the second time.

9And David said to Abishai, Destroy him not; for who can stretch forth his hand against Jehovah's anointed, and be guiltless?