Eruvin 49A

אף זו דברי רבי שמעון, אבל חכמים אומרים: שלשתן אסורות.

This teaching, that carrying objects from either of the outer courtyards into the middle courtyard is permitted, is also the statement of, i.e., in accordance with, the opinion of R' Shimon. But the Rabbis say: All 3 courtyards are prohibited, that is to say, carrying is prohibited from any of the courtyards to any of the others.

תניא כוותיה דרב יהודה אליבא דשמואל, אמר רבי שמעון: למה הדבר דומה לשלש חצירות הפתוחות זו לזו ופתוחות לרשות הרבים, עירבו שתים עם האמצעית ⁠— זו מביאה מתוך ביתה ואוכלת, וזו מביאה מתוך ביתה ואוכלת. זו מחזרת מותרה לתוך ביתה, וזו מחזרת מותרה לתוך ביתה.

It was taught in a baraita in accordance with the opinion of Rav Yehuda, in accordance with the opinion of Shmuel. R' Shimon said: To what is this comparable? It is comparable to 3 courtyards that open into one another, and that also open into a public domain. If the two outer courtyards established an eiruv with the middle one, a resident of one of the outer courtyards may bring food from a house in that courtyard and eat it in the middle courtyard, and likewise a resident of the other courtyard may bring food from a house in that courtyard and eat it in the middle courtyard. And similarly, this resident may bring leftovers from the house where he ate back into the house in that courtyard, and that resident may bring leftovers from the house where he ate back into the house in this courtyard.

אבל חכמים אומרים: שלשתן אסורות.

However, the Rabbis say: All 3 courtyards are prohibited. Since the residents of the outer courtyards are prohibited to carry from one outer courtyard to the other, this results in a place where carrying is prohibited, and such a place prohibits carrying in all 3 courtyards.