פירוש על עבודה זרה 102:10

Oshaia’s midrash is based on two verses which seem to contradict each other, for one mentions wood and stone and silver and gold whereas the second one mentions only silver and gold. The answer is that the verse teaches that for the items found “with them” to be prohibited they must be like the items found on them—decorative. Silver and gold are obviously decorative, but for the wood and stone to be prohibited they too must be decorative.
Below the Talmud will ask how this proves the halakhah in the mishnah. After all, the list of items in the first half could also be decorative. It seems to me that R. Oshaia’s midrash here originally proved a halakhah that was different from that found in the mishnah.