The Sabbath Commandment Existed Before Mount Sinai
"There is no evidence in the Bible of anyone keeping the Sabbath
before the time of Moses, nor are there any commands in the Bible
to keep the Sabbath before giving the law at Mt. Sinai."
                            Brian Garrison

Donna writes:  Even though the Sabbath is not specially mentioned,
we have inferential evidence that Noah observed the sabbath:

Genesis 8:6-12  PP6

   (1.) That Noah sent forth the dove the second time
seven days after the first time, and the third time was after
seven days too; and probably the first sending of her out was
seven days after the sending forth of the raven. This intimates
that it was done on the sabbath day, which, it should seem, Noah
religiously observed in the ark. Having kept the sabbath in a
solemn assembly of his little church, he then expected special
blessings from heaven, and enquired concerning them. Having
directed his prayer, he looked up, .
(from Matthew Henry's Commentary)

Even though the Sabbath is not specifically mentioned,
we have inferential evidence that Abraham observed the sabbath:

  "And I will make thy seed to multiply as the stars of heaven,
   and will give unto thy seed all these countries;
   and in thy seed shall all the nations of the earth be blessed;

Because that Abraham obeyed my voice, and kept my charge,
   my commandments, my statutes, and my laws."  Gen 26:4-5 (KJV)

The Manna is irrefutable evidence that God commanded Sabbath
observance BEFORE Mount Sinai:

Exod 16:15-36
15    And when the children of Israel saw it, they said one to
another, It is manna: for they wist not what it was. And Moses
said unto them, This is the bread which the LORD hath given you
to eat.

16    This is the thing which the LORD hath commanded, Gather
of it every man according to his eating, an omer for every man,
according to the number of your persons; take ye every man for
them which are in his tents.

17    And the children of Israel did so, and gathered, some more,
some less.

18    And when they did mete it with an omer, he that gathered
much had nothing over, and he that gathered little had no lack;
they gathered every man according to his eating.

19    And Moses said, Let no man leave of it till the morning.
20    Notwithstanding they hearkened not unto Moses; but some
of them left of it until the morning, and it bred worms, and stank:
and Moses was wroth with them.
21    And they gathered it every morning, every man according to
his eating: and when the sun waxed hot, it melted.
22    And it came to pass, that on the sixth day they gathered
twice as much bread, two omers for one man: and all the rulers of
the congregation came and told Moses.
23    And he said unto them, This is that which the LORD hath
said, To morrow is the rest of the holy sabbath unto the LORD: bake
that which ye will bake to day, and seethe that ye will seethe; and
that which remaineth over lay up for you to be kept until the morning.

24    And they laid it up till the morning, as Moses bade: and it
did not stink, neither was there any worm therein.

25    And Moses said, Eat that to day; for to day is a sabbath
unto the LORD: to day ye shall not find it in the field.

26    Six days ye shall gather it; but on the seventh day, which
is the sabbath, in it there shall be none.

27    And it came to pass, that there went out some of the people
on the seventh day for to gather, and they found none.

28    And the LORD said unto Moses,


29    See, for that the LORD hath given you the sabbath,
therefore he giveth you on the sixth day the bread of two days;
abide ye every man in his place, let no man go out of his place
on the seventh day.

30    So the people rested on the seventh day.

Donna Kupp