The manna did not descend on the Sabbath. Instead, a double portion descended on Friday. This was the only exception to G‑d’s directive not to save manna from one day for the next.
The Sabbath
שַׁבָּתוֹן שַׁבַּת קֹדֶשׁ לַה' מָחָר וגו': (שמות טז:כג)
[On Friday, Moses told the people,] “Tomorrow will be a day of rest, a holy Sabbath unto G‑d.” Exodus 16:23

This is the first explicit mention in the Torah of the obligation to observe the Sabbath. It is appropriate that the Sabbath is introduced in connection with the manna, for the Sabbath and the manna share a common purpose – to underscore our complete dependency upon G‑d as the true source of all sustenance. Belief that human effort is the sole determining factor for success makes it hard to justify giving up a full day’s income. Not working on the Sabbath is a clear affirmation of our faith that sustenance lies in G‑d’s hands and that our work is no more than a vessel through which G‑d’s blessings can flow.1