“First delight, then instruct.”
                                        
                                        Erst erfreuen, dann belehren. 
Karl Friedrich Schinkel and Gustav Friedrich Waagen in "On the Purpose of the Berlin Gallery" [Über die Aufgabe der Berliner Galerie] (1828); occasionally attributed to von Humboldt, who had quoted Schinkel and Waagen in a report. 
Misattributed