Albert Barnes Commentary Exodus 16:25

"And Moses said, Eat that to-day; for to-day is a sabbath unto Jehovah: to-day ye shall not find it in the field." — Exodus 16:25 (ASV)

Eat that today - The practical observance of the Sabbath was thus formally instituted before the giving of the law. The people were to abstain from the ordinary work of everyday life: they were not to collect food, nor, as it would seem, even to prepare it as on other days.