Found in 1 comment on Hacker News
HarryHirsch · 2018-10-18 · Original thread
Wikipedia would have you believe the contrary: https://en.wikipedia.org/wiki/Fugitive_peasants

"Stadtluft macht frei" and the related "year and a day" are still German proverbs. Eric Hansen made similar assertions here (popular history, but sounds plausible): https://www.amazon.com/-/dp/3596173248/

Fresh book recommendations delivered straight to your inbox every Thursday.