Then answered David and said to Ahimelech the Hittite, and to Abishai the son of Zeruiah, brother to Joab, saying, Who will go down with me to Saul to the camp? Abishai said, I will go down with you.
"The Lord shall smite him, or his day shall come to die"  (1 Samuel 26:10).  This from the mouth of David was a prophecy, fulfilled eventually in the death of Saul in battle.  At this point in David's life, he was honoring the prohibition in the Pentateuch against one's taking vengeance into his own hands, a lesson which was emphasized in his ears by Abigail.