Not true. The Sabbath was defined (previous to the giving of the Law, btw) by the falling of manna. That day that the manna did not fall, and the double portion stayed preserved from the day before, IS the Sabbath, IS the Seventh day. And it was kept by Judah from that time. If it were not so, then Yeshua would certainly have set us all straight... But He honored the Hebrew Sabbath.
What name does it give for the Sabbath. Does it mention Saturday or Sunday?