עַל־כֵּ֡ן לֹֽא־יֹאכְל֨וּ בְנֵֽי־יִשְׂרָאֵ֜ל אֶת־גִּ֣יד הַנָּשֶׁ֗ה אֲשֶׁר֙ עַל־כַּ֣ף הַיָּרֵ֔ךְ עַ֖ד הַיּ֣וֹם הַזֶּ֑ה כִּ֤י נָגַע֙ בְּכַף־יֶ֣רֶךְ יַעֲקֹ֔ב בְּגִ֖יד הַנָּשֶֽׁה׃
Therefore the children of Yisrael do not eat the sciatic nerve that is on the hollow of the thigh, to this day, because he touched the hollow of Yaakov’s thigh on the sciatic nerve.
Torah Temimah points to Chullin 101a.
גיד הנשה נוהג בשליל.
The sciatic nerve applies to a fetus.
The Gemara discusses whether the prohibition extends to the fetus found inside a slaughtered animal.
Derash on the range of the prohibition (Bavli).
The prohibition of the sciatic nerve applies also to a fetus.