Shemot 16:22 -23 On the 6th day of the week, the people gather mann, and notice that there is a double portion. The elders ask Moshe what is happening. In verse 23, Moshe explains that this is what G-d commanded regarding the gathering of mann on the 6th day of the week (i.e. take a double portion, and reserve some of it for Shabbat, the next day.)
Rash"i on verse 22, explains that Moshe didn't initially tell B'nai Yisra'el the rules regarding the mahn collection for Shabbat, until the elders came and specifically asked him.
My question - why not? Was Moshe trying to hide something? Was he careless? Did he have an "elder moment"?