We do not bring bikkurim other than from the Seven Species; not from dates of the mountains, not from fruits of the valleys, and not from oil-olives that are not of the choicest.  We do not bring bikkurim before Shavuos. The people of Mount Tzevoim brought their bikkurim before Shavuos, but [the Kohanim] did not accept ]the bikkurim] from them, because of that which is written in the Torah (Exodus 23:16): And the feast of the harvest, the first of your produce which you sow in the field.