answer: "ni dieu ni maitre"

I think your search is so difficult because you are looking at a very basic tenet of freethinkers which may not be possible to pin down. Note that back then the authority of the masters or kings was claimed to derive from gods, so the exclamation is somewhat redundant. I've seen some German early socialist/anarchist texts where "no masters no gods" or so is the underlying message.

Below I'm translating a snippet about artist Andre Breton. Let me know if you run into German that needs translating. I tried a (German) search for "Weder Gott noch Herr"

Martin Voelker

In the years after the war [Andre] Berton's sympathy for Anarchism becomes more visible. In 'Arcane 17' (1947) he tells of the strong sentiment that had been evoked when, as a child, he had discovered a simple inscription on a tomb stone: "Neither God nor Master".

In der Nachkriegszeit wird die Sympathie Bretons für den Anarchismus deutlicher. In Arcane 17 (1947) erzählt er von dem starken Gefühl, das er als Kind empfunden hat, als er im Friedhof auf einem Grabstein diese einfache Inschrift entdeckte: "Weder Gott noch Herr".