Afterward, when David heard of it, he said, "I and my kingdom are forever guiltless before the Lord for the blood of Abner son of Ner.
May the guilt fall on the head of Joab, and on all his father's house; and may the house of Joab never be without one who has a discharge, or who is leprous, or who holds a spindle, or who falls by the sword, or who lacks food!"
References for 2 Samuel 3:29
So Joab and his brother Abishai murdered Abner because he had killed their brother Asahel in the battle at Gibeon.
Then David said to Joab and to all the people who were with him, "Tear your clothes, and put on sackcloth, and mourn over Abner." And King David followed the bier.
They buried Abner at Hebron. The king lifted up his voice and wept at the grave of Abner, and all the people wept.
The king lamented for Abner, saying, "Should Abner die as a fool dies?
Your hands were not bound, your feet were not fettered; as one falls before the wicked you have fallen." And all the people wept over him again.
Then all the people came to persuade David to eat something while it was still day; but David swore, saying, "So may God do to me, and more, if I taste bread or anything else before the sun goes down!"
All the people took notice of it, and it pleased them; just as everything the king did pleased all the people.
So all the people and all Israel understood that day that the king had no part in the killing of Abner son of Ner.
And the king said to his servants, "Do you not know that a prince and a great man has fallen this day in Israel?
Today I am powerless, even though anointed king; these men, the sons of Zeruiah, are too violent for me. The Lord pay back the one who does wickedly in accordance with his wickedness!"