1 Samuel 26:9
And David said to Abishai, Destroy him not: for who can stretch forth his hand against the LORD’s anointed, and be guiltless? And David said to Abishai, Destroy him not: for who can stretch forth his hand against the LORD’s anointed, and be guiltless?
The verse belongs to the time after Abiathar son of Ahimelech escaped Saul's slaughter of the Lord's priests and fled to David, when David knew Doeg the Edomite would tell Saul, acknowledged that he had occasioned the death of all of Abiathar's father's house, and promised Abiathar safety with him because Saul sought both their lives. David speaks when Saul is asleep and defenseless in his power, with Abishai and his men urging him to kill Saul, a pressure he faced often when he had Saul in his power. He refuses to destroy Saul because Saul is the Lord's anointed ruler appointed by God, and to stretch forth the hand against him brings guilt.
He leaves Saul's judgment to God, who might strike him directly, let him die a natural death, or let him perish in battle. Instead of harming Saul, he takes Saul's spear and water and leaves him unharmed. Though David knew God had chosen him to be ruler in Israel, he still refused to harm Saul.
His humility and faithfulness kept him from taking the life of the ruler God had appointed, shown in his humble, irreproachable conduct in obedient service to Saul and in doing God's will, which was a constant rebuke to Saul's extravagant, rebellious course while Saul hunted him as a wild beast and made killing him the great object of his life. Rather than strike Saul, he chose to seek asylum and refuge among the Philistines with a prudent, humble course, by which he made even his enemies to be at peace with him, and he remained there until Saul died.