Eruvin 30A

אבל בגדי עשירים לעניים ⁠— לא.

But the clothing of the wealthy does not need to be 3 by 3 handbreadths in order to become ritually impure for the poor because even smaller pieces of cloth are significant for the poor. Therefore, the law with regard to the poor is not determined by the customary practice of the rich. So too, the law of eiruv pertaining to the rest of the world should not be determined by the customary practice of the Persians to eat roasted meat as a food in itself.

וכי תימא: הכא לחומרא והכא לחומרא, והתניא, רבי שמעון בן אלעזר אומר: מערבין לחולה ולזקן כדי מזונו. ולרעבתן, בסעודה בינונית של כל אדם. קשיא.

And if you say: Both here the ruling is stringent, and there the ruling is stringent, i.e., with regard to ritual impurity the halakha is stringent with respect to the poor and declares scraps of cloth that are only 3 by 3 fingerbreadths impure, but with regard to eiruv the halakha requires enough roasted meat to suffice for two meals as a food in its own right, in accordance with the practice of the Persians, then there is a difficulty: Wasn’t it taught in a baraita that R' Shimon ben Elazar says: One may establish an eiruv for an ill or elderly person with an amount of food that is enough for him for two meals, and if he eats less than the average person due to his sickness or age, a smaller amount of food is required in order to establish an eiruv on his behalf; however, for a glutton, we do not require food in an amount that would satisfy him but merely enough food for two meals measured according to an average meal for the typical person? This indicates that the halakha with respect to an eiruv is lenient and not stringent. The Talmud concludes: Indeed, this is difficult.