Exodus 16:23

Here is a plain intimation of the observing a seventh day sabbath, not only before the giving of the law upon mount Sinai, but before the bringing of Israel out of Egypt and therefore from the beginning. If the sabbath had now been first instituted, how could Moses have understood what God said to him, Exodus 16:4, concerning a double portion to be gathered on the sixth day, without making any express mention of the sabbath? And how could the people so readily take the hint, Exodus 16:22, even to the surprize of the rulers, before Moses had declared that it was done with regard to the sabbath, if they had not had some knowledge of the sabbath before? The setting apart of one day in seven for holy work, and in order to that for holy rest, was a divine appointment ever since God created man upon the earth.