2 Samuel 3:26-30

Joab left David and went into action. He sent messengers after Abner; they caught up with him at the well at Sirah and brought him back. David knew nothing of all this. When Abner got back to Hebron, Joab steered him aside at the gate for a personal word with him. There he stabbed him in the belly, killed him in cold blood for the murder of his brother Asahel. Later on, when David heard what happened, he said, “Before GOD I and my kingdom are totally innocent of this murder of Abner son of Ner. Joab and his entire family will always be under the curse of this bloodguilt. May they forever be victims of crippling diseases, violence, and famine.” (Joab and his brother, Abishai, murdered Abner because he had killed their brother Asahel at the battle of Gibeon.)