משנה אויף בראשית 32:33

[The prohibition of] the sciatic nerve is in force both within the land and outside it, both during the existence of the Temple and after it, in respect of both unconsecrated and consecrated [animals]. It applies to cattle and to wild animals, to the right and left hip. But it does not apply to a bird because it does not have a socket [on its hip]. It applies to a fetus. Rabbi Judah says: it does not apply to a fetus. And its [forbidden] fat is permitted. Butchers are not trustworthy with regard to the [removal of the] sciatic nerve, the words of Rabbi Meir. The sages say: they are trustworthy with regard to it as well as with regard to the [forbidden] fat.

It applies to clean animals but not to unclean. Rabbi Judah says, even to unclean animals. Rabbi Judah said: was not the sciatic nerve prohibited from the time of the sons of Jacob, and at that time unclean animals were still permitted to them? They replied, this law was ordained at Sinai but was written in its proper place.