Reference for Pesachim 43:3
מתיב רבי יצחק נפחא והרי גיד הנשה דרחמנא אמר (בראשית לב, לג) על כן לא יאכלו בני ישראל את גיד הנשה ותנן שולח אדם ירך לנכרי וגיד הנשה בתוכו מפני שמקומו ניכר
R'Isaac of Nappaha<span class="x" onmousemove="('comment',' Or, the smith. Many Rabbis were workers or tradesmen.');"><sup>6</sup></span> objected: But what of the nervus ischiadicus, though the Divine Law saith, Therefore the children of Israel eat not the sinew of the thigh-vein,<span class="x" onmousemove="('comment',' Gen. XXXII, 33.');"><sup>7</sup></span> yet we learned: A man may send the thigh [of an animal] to a heathen with the nervus ischiadicus in it, because its place is distinguishable!<span class="x" onmousemove="('comment',' The Jew need not remove the nervus ischiadicus before sending it, for fear that another Jew, seeing that the heathen had received it from a Jew, may think that the nerve has been removed and that it is all permitted, because one can easily recognize whether the nervus ischiadicus has been removed or not. Giving anything to a heathen is regarded as benefit, and we thus see that the benefit of this sinew is permitted, which conflicts with R. Abbahu's statement supra 21b.');"><sup>8</sup></span>