Reference for Bava Kamma 199:4
הי רבי מאיר אילימא רבי מאיר (ד' ל' מ' פ' סימן)
which apparently means that it was only R. Meir who maintained so whereas we did not hold in accordance with his view? — But he said to him: No; R. Meir maintained so and we hold with him. But to what [statement of] R. Meir [was the reference]? It could hardly be the one of R. Meir which we learned: If a judge in giving judgment [in a certain case] has declared innocent the person who was really liable or made liable a person who was really innocent, declared defiled a thing which was levitically clean, or declared clean a thing which was really defiled,<span class="x" onmousemove="('comment',' And it so happened that that thing was consequently mixed with clean things and this spoiled them all; v. Sanh. (Sonc. ed.) p. 210, nn. 6-8. ');"><sup>4</sup></span>