Bikkurim, Chapter 3, Mishnah 8. This mishnah deals with the distinction between the different levels of wealth among those who bring the bikkurim. It may well follow from the previous mishnah, which discussed the different levels of literacy, and here the levels of wealth are discussed.
The words of the Mishnah:
"Ha'ashirim mevi'in bikureihem b'kaltos shel kesef v'shel zahav" - the wealthy would bring their bikkurim in baskets of silver and of gold.
"V'ha'aniyim mevi'in osam b'salei netzarim shel aravah kelufah" - the poor would bring them in woven baskets made of peeled willow branches.
"V'hasalim v'habikkurim nitnu lakohanim" - the baskets, at least those of the poor, along with the bikkurim themselves, were both given to the kohanim.
The silver and gold baskets, however, as the Gemara says, were returned to the wealthy, since they were extremely valuable and it was not expected that they give them up, for this was not a one time bringing.
A note about the aravah:
The woven baskets of the poor were made of aravah. It is worth pointing out that the common English translation (willow) is not precise: this refers to our aravos, the very same aravos we use on Sukkos.
In summary: The mishnah distinguishes between the wealthy, who bring their bikkurim in baskets of silver and gold, and the poor, who bring them in woven baskets of peeled aravah. The baskets and the bikkurim are given to the kohanim, while the silver and gold baskets are returned to their owners. From here comes an interesting point made by the Gemara, connected to the familiar expression: the poor become poorer, since they lose their basket, while the wealthy get their basket back.