When Saul saw David going out against the Philistine, he said to Abner, the commander of the army, "Abner, whose son is this youth?" And Abner said, "As your soul lives, O king, I do not know."
1 Samuel 17:55
Surrounding context
17:54 And David took the head of the Philistine and brought it to Jerusalem, but he put his armor in his tent.
17:55 When Saul saw David going out against the Philistine, he said to Abner, the commander of the army, "Abner, whose son is this youth?" And Abner said, "As your soul lives, O king, I do not know."
17:56 So the king said, "Inquire whose son this young man is."