But the king spared Mephibosheth, the son of Jonathan the son of Saul, because of the oath of the Lord which was between them, between David and Saul’s son Jonathan.

Then David said, "Is there yet anyone left of the house of Saul, that I may show him kindness for Jonathan's sake?" Now there was a servant of the house of Saul whose name was Ziba, and they called him to David; and the king said to him, "Are you Ziba?" And he said, "I am your servant." The king said, "Is there not yet anyone of the house of Saul to whom I may show the kindness of God?" And Ziba said to the king, "There is still a son of Jonathan who is crippled in both feet." read more.
So the king said to him, "Where is he?" And Ziba said to the king, "Behold, he is in the house of Machir the son of Ammiel in Lo-debar." Then King David sent and brought him from the house of Machir the son of Ammiel, from Lo-debar. Mephibosheth, the son of Jonathan the son of Saul, came to David and fell on his face and prostrated himself. And David said, "Mephibosheth." And he said, "Here is your servant!" David said to him, "Do not fear, for I will surely show kindness to you for the sake of your father Jonathan, and will restore to you all the land of your grandfather Saul; and you shall eat at my table regularly."