פירוש על עבודה זרה 46:10

The Talmud now tries another tack. Maybe the rabbis too are concerned about bestiality. But they assume that a non-Jew will not have sex with the red heifer because that would be a great loss. But when it comes to other sacrifices, maybe they would have sex with the animal. After all, it’s not such a big financial loss if the Jew won’t buy it.

According to Shila, R. Eliezer disqualifies a red heifer bought from a non-Jew because of the verse, “Speak to the children of Israel.” But the same language is used in connection with offerings for the Temple and non-Jews do seem to be allowed to make donations to the Temple.