And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made. Genesis 2:3
"But what of the statement that: Their doctors universally date the 
Sabbath from the Mosaic legislation, generally referring its commencement to Exodus 15:25: “There He made a statute,” etc.
If it were true that “their doctors” referred the institution of the Sabbath to the time when the Israelites were at Marah, that would not make it true, when the inspired record plainly tells us that it was instituted at creation.
It is not an unheard-of thing for “doctors” to be mistaken. Whatever the Talmud may or may not say concerning an ante-Mosaic Sabbath, Josephus says:
Accordingly Moses says that in just six days the world and
Accordingly Moses says that in just six days the world and
"...all that is therein was made; and that the seventh day was a
rest, and a release from the labor of such operations;—
whence it is that we celebrate a rest from our labors on that
day, and call it the Sabbath."
rest, and a release from the labor of such operations;—
whence it is that we celebrate a rest from our labors on that
day, and call it the Sabbath."
*It is a matter for curiosity,
---however a man who can see no proof whatever for Sabbath observance, in Genesis 2:3, which speaks directly on a point,
---can find in Exodus 15:25 evidence of its institution, when the latter text makes no hint of the Sabbath.
But the human mind, when controlled by prejudice, is not subject to laws." E.J. Waggoner
