Chullin 39 - Shechitah for the Sake of an Idolater
If an idolater asks a Jew to perform shechitah to the idolater's animal, the shechitah is valid. Rabbi Eliezer declares the meat forbidden. According to Rabbi Eliezer, the unspoken thought of an idolater is to dedicate the animal for his idol. Therefore, even if he sells the animal to the Jew but keeps a small part for the himself, the complete animal is prohibited. Actually, the first teacher agrees that the intent of the idolater takes effect, only the first teacher requires that it be spoken, and according to Rabbi Eliezer, even the thought is sufficient, and we can even assume that thought.
Rabbi Yose disagrees and claims that the owner's thought has no effect at all. He argues thus. If in the Temple, where the kohen's intent is pervasive and makes or breaks a sacrifice, the owner's intent does not matter, then certainly in the case of regular food, the owner's intent is ineffective.
Rabbi Eliezer answers that firstly, when the Torah uses the term "one who brings the sacrifice," it means both the kohen and the owner. Secondly, just as in the Temple, the owner's idolatrous intent matters, so too it matters for regular shechitah outside the Temple.
Art: Jacob Willemsz de Wet the Elder - Figures Offering A Sacrifice In A Temple