Joshua 5:11

From the day after the Pesach. This was the day of waving the Omer, for they sacrificed the Omer first. From the seventh day of Adar, the day when Moshe died, when the manna stopped falling, they were sufficiently supplied with the manna which was in their vessels which they gathered on the seventh of Adar, as it is said, ‘They ate the manna for forty years.’ But these forty years lacked thirty days— for the manna began to fall on the fifteenth day of Iyar. We must say therefore that in the [matzo] cakes the Bnei Yisroel took with them from Egypt, they tasted the taste of manna.

They ate of the produce (meavor) of the country: They ate matza and parched grain from the old grain, since the new grain was forbidden to them until after the bringing of the omer on the sixteenth of Nissan. And even for matza, matza is forbidden from the new grain... And from where did they have old grain? From that which the merchants of the [other] nations sold to them. And the word meavor proves that it was from the old grain. For I say that the grain that is from the year that passed (avrah) is called avor, and [grain from] the next year is called produce (tevuah).

from the morrow of Passover: That is the night of the fifteenth of Nissan and its day. For the Passover sacrifice is offered on the fourteenth, and its morrow is the fifteenth. And likewise, "on the fifteenth day of the first month - on the morrow of Passover - the Children of Israel went out of Egypt" (Numbers 33:3).