Which text became well known for using Haydn's melody associated with Emperor Franz II?

The text associated with Haydn's melody known for its connection to Emperor Franz II is indeed well recognized as the German national anthem, which is based on the tune from Haydn's string quartet. This melody, composed in 1797, was initially used for a hymn honoring the Emperor and later became the foundation for the anthem known as "Das Lied der Deutschen" (The Song of the Germans).

Over time, only the third stanza of this song was adopted as the official national anthem of Germany after World War II, while the other stanzas were deemed unsuitable due to their association with German nationalism during the 19th and early 20th centuries. Haydn's composition has thus played a significant role in Germany's musical heritage, making the connection between the melody and the German national anthem an important historical point.