John Gill Commentary 1 Samuel 24:4

"And the men of David said unto him, Behold, the day of which Jehovah said unto thee, Behold, I will deliver thine enemy into thy hand, and thou shalt do to him as it shall seem good unto thee. Then David arose, and cut off the skirt of Saul`s robe privily." — 1 Samuel 24:4 (ASV)

And the men of David said unto him
Some of his principal men, who were about him, and near him, such as Joab and Abishai:

behold the day of which the Lord said unto thee :
now the time was come that he spoke of to him by Samuel, or Gad, or to himself directly:

behold, I will deliver your enemy into your hand ;
and such was Saul, as appeared by his seeking to take away his life; and now he was in the hand of David to take away his life, if he pleased:

that you may do to him as it shall seem good unto you ;
an opportunity of this kind now offered:

then David arose ;
from that part of the cave in which he was, the further part of it:

and cut off the skirt of Saul's robe privily ;
unawares to him, and unobserved by him, which might be easily done, if Saul was asleep, and it is probable he was; and by the same way it may be accounted for that he did not hear the discourse that passed between David and his men.