1 Samuel 17:53-57

Then the sons of Israel returned from their close pursuit of the Philistines, and plundered their camps.

And David took the Philistine’s head and brought it to Jerusalem, but he put his weapons in his tent.

Now when Saul had seen David going out against the Philistine, he said to Abner the commander of the army, “Abner, whose son is this young man?” And Abner said, “By your life, O king, I do not know.”

And the king said, “You then, ask whose son the youth is.”

So when David returned from killing the Philistine, Abner took him and brought him before Saul with the Philistine’s head in his hand.