Abishai - He was son of Zeruiah, David's sister, but probably about the same age as David. He because very famous as a warrior 2 Samuel 23:18, but was implicated with his brother Joab in the murder of Abner in retaliation for the death of their brother Asahel 2 Samuel 3:30.

let me smite him … even to the earth at once—The ferocious vehemence of the speaker is sufficiently apparent from his language, but David's magnanimity soared far above the notions of his followers. Though Saul's cruelty and perfidy and general want of right principle had sunk him to a low pitch of degradation, yet that was no reason for David's imitating him in doing wrong. Besides, he was the sovereign; David was a subject. Though God had rejected him from the kingdom, it was in every way the best and most dutiful course, instead of precipitating his fall by imbruing their hands in his blood and thereby contracting the guilt of a great crime, to wait the awards of that retributive providence which sooner or later would take him off by some sudden and mortal blow. He who, with impetuous haste was going to exterminate Nabal, meekly spared Saul. But Nabal refused to give a tribute to which justice and gratitude, no less than custom, entitled David. Saul was under the judicial infatuation of heaven. Thus David withheld the hand of Abishai; but, at the same time, he directed him to carry off some things which would show where they had been, and what they had done. Thus he obtained the best of victories over him, by heaping coals of fire on his head.

for who can stretch forth his hand against the Lord's anointed, and be guiltless? since Saul was king, and appointed to that office by the Lord, and was anointed by his order for it, and invested with it by him, his person was sacred, and not to be touched; nor could his life be taken away by any without being guilty of a very great crime indeed, which it might be justly expected the Lord would resent and punish.

(e) That is, in his own private cause: for Jehu slew two kings at God's appointment, 2Ki 9:24.