Reference for Rosh Hashanah 57:2

מיתיבי היה עובר אחורי בית הכנסת או שהיה ביתו סמוך לבית הכנסת ושמע קול שופר או קול מגילה אם כוון לבו יצא ואם לאו לא יצא וכי כוון לבו מאי הוי היאך לא קא מיכוין אדעתא דידיה

The following was raised in objection against this view: IF HE WAS PASSING BEHIND THE SYNAGOGUE, OR IF HIS HOUSE WAS ADJOINING THE SYNAGOGUE AND HE HEARD THE SOUND OF THE SHOFAR OR THE READING OF THE MEGILLAH, IF HE PUT HIS MIND TO IT HE THEREBY PERFORMED HIS RELIGIOUS DUTY, BUT IF NOT HE DID NOT. And if he did put his mind to it, what difference does it make [on your theory], seeing that the other [the performer] was not consciously performing for him? - We are here speaking of a congregational reader who performs consciously for all.

Jastrow