“The Scriptures mention the Sabbath much sooner than Adam fell into sin. Was it not appointed at that time that he should work six days and rest on the seventh? … Nature teaches that the working classes…who have spent the whole week in their work…absolutely require a day in which they can…rest and refresh themselves and…attend to the worship of God.”
~Martin Luther, Larger Catechism.
Per F.N. Lee: “Compare too the citation in J.N. Andrews & L.R. Conradi: History of the Sabbath and the First Day of the Week, Washington, Review & Herald, 1912, pp. 609 & 627”
Source: qtd. in “The Protestant Reformation on Sabbath-Keeping” by Rev. Prof. Dr. F.N. Lee at http://www.dr-fnlee.org/the-protestant-reformation-on-sabbath-keeping/