Reference for Chullin 7:2

שׁוֹלֵחַ אָדָם יָרֵךְ לְנָכְרִי שֶׁגִּיד הַנָּשֶׁה בְתוֹכָהּ, מִפְּנֵי שֶׁמְּקוֹמוֹ נִכָּר. הַנּוֹטֵל גִּיד הַנָּשֶׁה, צָרִיךְ שֶׁיִּטֹּל אֶת כֻּלּוֹ. רַבִּי יְהוּדָה אוֹמֵר, כְּדֵי לְקַיֵּם בּוֹ מִצְוַת נְטִילָה:

It is lawful to send to a non-Israelite a thigh having the ‏גיד הנשה‎ [sciatic nerve] yet within it, because its existence is easily ascertained. In removing the ‏גיד הנשה‎ [sciatic nerve] the whole sinew must be carefully cut out. R. Judah saith, "It suffices if enough was removed so as to fulfill the precept."

Jastrow