פירוש על קידושין 114:5

The mishnah does not agree with R. Shimon b. Judah who holds that just as one may derive benefit from meat that was not properly slaughtered (one can use it to feed one’s animals), so too one may derive benefit from meat cooked in milk. I should note that this is not the accepted opinion—according to halakhah, one may not derive any benefit from meat cooked in milk.