Charles Ellicott Commentary 1 Samuel 26:9

"And David said to Abishai, Destroy him not; for who can put forth his hand against Jehovah`s anointed, and be guiltless?" — 1 Samuel 26:9 (ASV)

Against the Lord’s anointed. —David—taught, no doubt, by the prophet Samuel—looked upon the person of Saul as made sacred and inviolable by the royal anointing. Through the anointing Saul had become the possession of Jehovah; only Jehovah, then, could lawfully take away that sacred life. This he elaborates in the next verse. It is possible that these exalted sentiments respecting the Divine rights of kings were not uttered by David while standing in the dark night among Saul’s soldiers by the sleeping king, but subsequently, when he and Abishai were talking the incident over together.