2 Samuel 3:24-27

24So Joab went to the king and said, “What have you done? Look, Abner came to you. Why did you let him go? Now he is gone!

25You know Abner son of Ner; he came to deceive you and observe your movements and find out everything you are doing.”

26Joab then left David and sent messengers after Abner, and they brought him back from the cistern at Sirah. But David did not know it.

27Now when Abner returned to Hebron, Joab took him aside into an inner chamber, as if to speak with him privately. And there, to avenge the blood of his brother Asahel, Joab stabbed him in the stomach, and he died.