Beis Kislev, 5777
Location: Elizabeth, New Jersey
A blind Jew who would walk around with the assistance of a guide dog was faced with a dilemma. He desired to attend services in shul, but it didn't seem respectable to enter a mikdash me'at with a dog (or with any other animal, for that matter). On the other hand, that was the only way he would be able to participate in all of the devarim shebi'kedushah taking place in shul. Was he allowed to enter the shul with his dog?
The man presented his query to the local Rov, R. Pinchas Mordechai Teitz OBM, who in turn asked the opinion of HaRav Moshe Feinstein OBM.
In his teshuvah, R. Moshe cites a Yerushalmi (Megilah 3:3) that states that talmidei chachomim may make use of a shul for their personal needs. The Yerushalmi continues that Rav Imi instructed the schoolteachers (who taught in shul): "Even if a 'mediocre' talmid chochom arrives to the shul, allow him to enter along with his donkey and utensils." From this Gemara we can deduce that bringing an animal into shul is no worse than making use of it in other ways (such as through eating or drinking there). Since our shuls today are built with the stipulation that they may be used for other purposes (even by those who are not talmidei chachomim), it follows that one may bring an animal into a shul, at least in a case of a sha'as hadechak (such as ours).
R. Moshe brings another interesting proof as well. The Gemara (Brachos 62a) relates that Abayei's mother raised a sheep that would constantly accompany him. (This way he would not enter thebeis hakiseialone and would be protected from mazikin.) Since Abayei certainly spent most of his day in the beis midrash, the sheep probably accompanied him there as well.
R. Moshe concludes that the man was allowed to enter the shul with his dog, but he recommended that he sit near the entrance, to avoid disturbing the congregation.
When R. Moshe's teshuvah was printed in the first volume of Igros Moshe in 1959, Rabbi Menachem Mendel Kasher OBM, compiler of Torah Shleimah, sent him a letter with a number of comments on the sefer, including this particular teshuvah. R. Moshe's heter was based on the premise that a dog is no worse than a donkey or sheep. R. Kasher argues with this premise.