For the source text click/tap here: Bava Metzia 45
To download, click/tap here: PDF
The Gemara cites a Mishnah (Ma'aser Sheni 2:7) in which Beis Shamai and Beis Hillel argue as to whether one may redeem silver coins of Ma'aser Sheni with gold coins. Beis Shamai forbids it and Beis Hillel allows it.
The Gemara explains this Mishnah in three different ways. According to all three explanations, Beis Hillel views gold as merchandise in relation to silver, as Beis Hillel permits one to redeem silver coins of Ma'aser Sheni with gold coins even though Ma'aser Sheni may be redeemed only with currency (outside of Yerushalayim) and not with Peros (merchandise).
The view of Beis Hillel (whose view is almost always accepted as the Halachah) in this regard clearly conflicts with the ruling of all of the Poskim.
We explore the development of Maaser Sheni a uniquely rabbinic law.