פירוש על עבודה זרה 47:3

An even greater difficulty is that the following year Dama ben Natina sold them a red heifer. This proves that not only is Shila wrong, but even R. Eliezer himself. The Talmud answers that the red heifer was not bought directly from Dama. Dama sold it to some Jewish merchants and they sold it to the sages. Jewish middlemen—they always find a way don’t they!