1 Samuel 17:55

As Saul had watched David going out to confront the Philistine, he said to Abner the commander of the army, “Abner, whose son is this young man?” “As surely as you live, O king,” Abner replied, “I do not know.”

¶ And when Saul saw David go forth against the Philistine, he said unto Abner, the captain of the host, Abner, whose son is this youth? And Abner said, As thy soul liveth, O king, I cannot tell.