Chulin 2:7-8

Chulin 2:7

If one slaughters a non-Jew’s animal for him, the slaughter is valid (even though the owner intends to use it for idolatrous purposes); Rabbi Eliezer declares it invalid. Rabbi Eliezer explained that even if the Jew slaughtered the animal so that its non-Jewish owner might eat the lobe of the liver, it’s invalid because of its owner’s general ongoing idolatrous inclinations. Rabbi Yosi demonstrated through a kal v’chomer (an argument a fortiori) that the owner’s intentions do not invalidate the slaughter, as follows: when it comes to sacrifices, where intention can invalidate them, it all depends on the one performing the service (rather than on the one who brought the offering). All the more so with secular food, where intention does not invalidate, everything should depend on the one performing the slaughter (as opposed to the animal’s owner).

Chulin 2:8

If a person slaughters an animal in the name of mountains, hills, seas, rivers or deserts, the slaughter is invalid (because of the idolatrous intention). If two people hold the knife and slaughter an animal together, one in the name of any of these things and the other for legitimate reasons, the slaughter is invalid.