John Gill Commentary 1 Samuel 26:8

"Then said Abishai to David, God hath delivered up thine enemy into thy hand this day: now therefore let me smite him, I pray thee, with the spear to the earth at one stroke, and I will not smite him the second time." — 1 Samuel 26:8 (ASV)

Then said Abishai to David
Seeing Saul fast asleep, and a spear so near him:

God has delivered your enemy into your hand this day :
or at this time, properly it was night:

now therefore let me smite him, I pray you, with the spear ;
with Saul's own spear, which was stuck in the ground at his bolster. He remembered that David would not put forth his hand to stay him before, when he had an opportunity; and since now another offered, he did not move it to him to do it, but begged leave to do it himself; which he might think would be granted, since there was such a remarkable hand of Providence in it, which seemed to direct to such a step:

even to the earth at once, and I will not [smite] him the second time ;
signifying, that he would give such a home blow or thrust, that the spear should pierce through him, and fasten him to the ground, that there would be no need to repeat it.