Related על גיטין 122:13

One who [brings his grain to be] milled at the place (i.e., the mill) of an am ha'aretz or the place of a Samaritan, he need not be concerned about impurity (cf. Dem. 3:4). One who [brings his grain to be] milled at the place of a Gentile, behold, he needs to be concerned about impurity.