1 Samuel 17:55

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.

Ver. 55. Whose son is this?] Saul being of a weak brain by reason of his frantic fits, and withal full of business, had, belike, forgotten David, who might be now much altered in his visage and habit, and never haply otherwise taken notice of by Saul than as princes use to do of musicians or servants.