פירוש על עבודה זרה 138:8

The last clause of the mishnah does not contain a dispute between the rabbis and R. Shimon b. Gamaliel and yet seems to follow R. Shimon b. Gamaliel’s opinion. This indicates, according to Rava, that the halakhah follows Rabban Shimon b. Gamaliel. In other words, the editor of the mishnah hinted here that the halakhah follows Rabban Shimon b. Gamaliel.