1 Samuel 24:3-7

And he came to the sheepcotes by the way, where was a cave; and Saul went in to cover his feet: and David and his men remained in the sides of the cave. And the men of David said unto him, Behold the day of which the LORD said unto thee, Behold, I will deliver thine enemy into thine hand, that thou mayest do to him as it shall seem good unto thee. Then David arose, and cut off the skirt of Saul's robe privily. And it came to pass afterward, that David's heart smote him, because he had cut off Saul's skirt. And he said unto his men, The LORD forbid that I should do this thing unto my master, the LORD's anointed, to stretch forth mine hand against him, seeing he is the anointed of the LORD. So David stayed his servants with these words, and suffered them not to rise against Saul. But Saul rose up out of the cave, and went on his way.