1 Samuel 17:55 in the King James Version
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.
Context
54 David took the head of the Philistine and brought it to Jerusalem, but he put his armor in his tent.
55 When Saul saw David go out against the Philistine, he said to Abner, the captain of the army, “Abner, whose son is this youth?” Abner said, “As your soul lives, O king, I can’t tell.”
56 The king said, “Inquire whose son the young man is!”