Eruvin 81B

ומודים בשאר כל האדם, שזכו לו מעותיו. שאין מערבין לאדם אלא מדעתו.

And the Rabbis concede with regard to all other people, apart from grocers and bakers, that if one gave them money for the food of an eiruv, his money confers possession upon him, as one may establish an eiruv for a person only with his knowledge and at his bidding. With regard to a grocer or baker, the person giving the money does not intend to appoint the grocer or the baker as his agent and the money itself does not effect an acquisition, and consequently, he did not accomplish anything. With regard to anyone else, however, there is no doubt that he must have intended to appoint him his agent, and his act is effective.

אמר רבי יהודה: במה דברים אמורים בעירובי תחומין, אבל בעירובי חצירות ⁠— מערבין לדעתו ושלא לדעתו, לפי שזכין לאדם שלא בפניו, ואין חבין לאדם שלא בפניו.

R' Yehuda said: In what case is this statement said? It is said with regard to a joining of Shabbat boundaries, but with regard to a joining of courtyards, one may establish an eiruv for a person either with his knowledge or without his knowledge. The reason is because one may act for a person’s benefit in his absence, but one may not act to a person’s disadvantage in his absence. As a participant in a joining of courtyards benefits from his inclusion in the eiruv, his consent is not required. However, with regard to a joining of Shabbat boundaries, although it enables one to go farther in one direction, he loses the option of traveling in the opposite direction. When an action is to a person’s disadvantage, or if it entails both benefits and disadvantages, one may act on that person’s behalf only if he has been explicitly appointed his agent.