Albert Barnes Commentary Exodus 16:22

"And it came to pass, that on the sixth day they gathered twice as much bread, two omers for each one: and all the rulers of the congregation came and told Moses." — Exodus 16:22 (ASV)

Twice as much bread - See (Exodus 16:5).

From this passage and from (Exodus 16:5) it is inferred that the seventh day was previously known to the people as a day separate from all others, and if so, it must have been observed as an ancient and primeval institution.