Midrash su Numeri 9:1

(Bamidbar 9:1) "And the L-rd spoke to Moses in the desert of Sinai in the second year after their going out from the land of Egypt, in the first month (Nissan), saying": This verse is in praise of Israel (to indicate) that they were encamped before Mount Sinai for eleven months, and to teach that there is no "before and after" (i.e., chronological order) in the Torah. For in the beginning of this Book it is written (1:1) "And the L-rd said to Moses in the desert of Sinai in the tent of meeting on the first day of the second month (Iyyar), and here it is written "in the first month" — to teach that there is no "before and after" in the Torah. Rebbi says: This is not needed (for this teaching), for it is already written (Shemot 16:35) "And the children of Israel ate the manna for forty years until they came to an inhabited land" — and they had not yet done so.