2 Samuel 24:3, 18

But Joab said to the king, “May the LORD your God add to the people a hundred times as many as there are, and let the eyes of my lord the king see it; but why does my lord the king want to do this thing?”

Then Gad [the prophet] came to David that day and said to him, “Go up, set up an altar to the LORD on the threshing floor of Araunah the Jebusite [where you saw the angel].”