I will show kindness unto Hanun the son of Nahash - We do not know exactly the nature or extent of the obligation which David was under to the king of the Ammonites; but it is likely that the Nahash here mentioned was the same who had attacked Jabesh-gilead, and whom Saul defeated: as David had taken refuge with the Moabites, ( 1 Samuel 22:3;), and this was contiguous to the king of the Ammonites, his hatred to Saul might induce him to show particular kindness to David.
The history does not record any instance of Nahash‘s kindness to David, but the enmity of the house of Nahash against Saul may have disposed him favorably toward Saul‘s enemy David, and if there was any family connection between David‘s house and Nahash 2 Samuel 17:25 this may have increased the friendship.