Reference for Pesachim 178:4

אמרי לא דעות שאני דא"נ תרוייהו כחד מבני חבורה הוא דאכלי מצי אמרי לי' דלא ניחא לן אינש נוכרא גבן

then let this one be as though he is quick-handed? - I will tell you: That is not so, [for] characters differ, for even if both of them together eat [only] as much as one member of the company, they can say to him that they are not willing to have a stranger with them. Come and hear: If the attendant ate as much as an olive at the side of the oven, if he is wise he eats his f of it; but if the members of the company wish to do him a favour, they come and sit at his side and eat: this is R'Judah's opinion.<span class="x" onmousemove="('comment',' V. supra ');">⁹</span> Thus, only if they wish, but not if they do not wish.

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