Rudolf Schock & Karl Ridderbusch 'Der Mond ist aufgegangen/The moon has risen' 1956 & 1983 

IN WORD AND DEED
RUDOLF SCHOCK has never taught singing in a formal sense.
But in word and deed, he has fully inspired and/or encouraged younger singing colleagues - according to their interviews and life stories.
The most striking was his discovery during a talent show in 1956 of the later world famous opera bass KARL RIDDERBUSCH. Schock part-funded Ridderbusch for his singing training.
In a modest amateur recording from Düsseldorf in November 1983, both singers can be heard in two couplets of the well-known, fascinating song "Der Mond ist aufgegangen (The moon has risen)" by Matthias Claudius (1779) & Johann Abraham Peter Schulz (1790).