The scene and verse are from the second act of "Siegfried", the third of four Operas by Richard Wagner that premiered in Bayreuth in 1876.
The entire Opera is called "Der Ring des Nibelungen"
(The Ring of the Nibelungs) from Norse mythology.
The porcelain stein has a transfer scene of Siegried in the
presence of the Dragon, Fafner, and the Nibelungen, Mime, and has a lithophane
(scene visible when the stein is empty and held up to the light) ca. 1900.
This verse is spoken (sung) by Mime, who raised the human boy Siegfried
as a foster child, while offering him a poisoned drink.