John Calvin on Exodus 16:5

5. And it shall come to pass. Because mention is immediately made of the Sabbath, some would confine to its observance what is said respecting the law, and extract this sense from it, that God made the experiment whether the people would faithfully observe the rest enjoined to them on each seventh day. But there is a poorness in this explanation. The fact is, that after God had promised daily supplies to His people, He now adds the exception, viz., that on the sixth day they should collect a double quantity, and lay aside half of it for the use of the Sabbath. Thus the seventh day was really hallowed before the promulgation of the Law, although it is questionable whether it had already been observed by the patriarchs. It appears probable that it was; but I am unwilling to make it a matter of contention.