2 Samuel 3:22-23
22-23Soon after that, David's men, led by Joab, came back from a field assignment. Abner was no longer in Hebron with David, having just been dismissed with David's blessing. As Joab and his raiding party arrived, they were told that Abner the son of Ner had been there with David and had been sent off with David's blessing.
24-25Joab went straight to the king: "What's this you've done? Abner shows up, and you let him walk away scot-free? You know Abner son of Ner better than that. This was no friendly visit. He was here to spy on you, figure out your comings and goings, find out what you're up to."