When Paroh pleads with Moshe to end the plague of hail and all that accompanied it, Moshe responds by telling him that he will leave the city and call out there to Hashem, who will then have the plague cease (Shemot 9:29). Rashi (s.v. ketzeiti), citing the Midrash in Shemot Rabbah (12:5), points out that Moshe did not want to pray to Hashem within the city limits because the place was full of that which the Egyptians worshipped as part of their idolatrous religious observance. As for why this concern surfaced only at this point, regarding the plague of hail, which was already, after all, the seventh plague, the Ramban there (s.v. ketzeiti) explains that this was in fact a concern when Moshe prayed regarding the earlier plagues as well, but it was mentioned specifically here because this time Moshe had to inform Paroh that he would be leaving the city since he had requested that Moshe pray immediately, which he could not do (see also Da’at Zekeinim MiBaalei HaTosafot, s.v. ketzeiti). The Netziv, in one of his teshuvot (Shu”t Meishiv Davar 1:10, s.v. aval), suggests that Moshe usually prayed in one of the “Shuls” which the Jewish people had set up for their community in Egypt, and he was therefore unconcerned about the Egyptian religious objects which were outside, but this time, because of the nature of this particular plague, he wanted to pray outdoors.

The Terumat HaDeshen (No. 6) discusses whether one who is traveling on a journey and will reach his destination with enough time to daven there, but is aware that the town he is heading towards is completely non-Jewish with no suitable place to daven, might be better off stopping on the side of the road and davening in that more “neutral” location. Referring to the aforementioned Midrash, he states that if it is indeed possible for the traveler to find a place to daven along the road where he will not be disturbed or interrupted, it is preferable for him to do so, because the non-Jewish town, and even the inn where he would stay, is most likely filled with the religious symbols of the non-Jews who reside there, in the form of paintings, engravings in the walls, statues and the like. If, however, there is no appropriate place on the road for him to daven, he should do so at the inn where he stays, especially if he can find a private room or corner there where he will not be distracted.

In the Shulchan Aruch (Orach Chaim 94:9), the Rama rules accordingly; the Mishnah Berurah (No. 29) cites the precedent from Moshe presented above, but then adds (No. 30) that in the final analysis, the main thing is to find a place where one can daven undisturbed, as the problem of idolatrous images in most towns where Jews currently reside is virtually unavoidable. He notes, though, that if there are such images on the very wall towards which one is davening, one should turn and face a different direction (although he would then not be facing towards Eretz Yisrael). Alternatively, the person may cover the non-Jewish religious symbol so it is not visible (see Kaf HaChaim to Orach Chaim 113:27) or, if there is no other option, he may simply close his eyes while davening, as pointed out by the She’arim Metzuyanim BeHalachah on the Kitzur Shulchan Aruch (18:7). It should be stressed that this situation can come up even nowadays when one is in certain hospitals or other public places.

A related question is raised regarding the conversion of a building used for non-Jewish worship into a Shul. The Shulchan Aruch (Orach Chaim 154:11) states that candles designated for idolatrous religious worship may not subsequently be used in a Shul; the Magen Avraham (No. 17) adds that in a similar vein, any item associated with non-Jewish religious service may not be used in a Shul, but he does cite a position that one may indeed daven in a building which had previously been used by others as a house of worship, as the building itself was not worshipped. The Elyah Rabbah there (No. 15) suggests, though, that this may be permissible on a one-time or temporary basis, but it would not be proper to use such a building as a permanent Shul. The Dagul MeRevavah, commenting on that ruling in the Magen Avraham (s.v. u’vemasechet), points to a statement by Tosafot in Megillah (6a, s.v. teratriyot) which appears to indicate that it is improper to turn a house of worship used for another religion into a Shul at all; the Chatam Sofer, in his comments to the Shulchan Aruch there makes the same reference and expands the point in a teshuvah (Shu”t Chatam Sofer, Orach Chaim No. 42), concluding that while it is acceptable to follow the lenient position, it is preferable to be stringent and avoid using such a building as a Shul. The Maharam Schick (Shu”t Maharam Schick, Yoreh De’ah No. 154) likewise affirms that it is improper to establish a Shul in a place utilized for other forms of religious service.

Rav Yosef Shaul Nathanson (Shu”t Sho’el U’Meishiv I:3:72) proposes a distinction based upon the nature of the religious worship performed in the building, suggesting that if there were never any religious symbols or icons used there (as in the case of a Muslim house of worship), it is permissible to use the place as a Shul. Indeed, he adds, it would in fact be a mitzvah to do so, as a means of sanctifying Hashem’s Name, especially in light of the fact that we believe that in the future, all nations will recognize Hashem and properly serve Him alone, in which case other houses of worship will in any event become places in which to daven to Hashem. If, however, the place contained symbols like the Christian cross, which people often bow to, many authorities are stringent, considering that to be similar to an idol (see the Rama in Yoreh De’ah 141:1 and Shu”t Minchat Elazar 1:53), though some disagree with that assertion (see Shu”t Mahari Assad, Yoreh De’ah No. 170).

The Mishnah Berurah (Orach Chaim 154:45) writes that the prevalent custom appears to be to take the lenient position here and allow a Shul to be established in a building previously used by another religious group, though he adds in the Biur Halachah (s.v. nerot) that one should not do so if actual religious images were used there. Rav Moshe Feinstein (Shu”t Igrot Moshe, Orach Chaim 1:49) is clearly uncomfortable with allowing the use of such a building for a Shul at all, maintaining that it is inappropriate to perform a mitzvah in such a fashion, but he does allow davening in such a Shul if it was already established or if the structure of the building was changed to the extent that it is no longer recognizable as the same building. In another teshuvah there (Orach Chaim 1:31), Rav Moshe Feinstein writes that any leniency in this matter is applicable only if the building in question has been purchased by those who wish to use it as a Shul, not if it is merely rented.

Finally, there is a question about davening in a room which has other religious symbols in the room above it or opposite it; the Taz (Orach Chaim 151:4) writes that one should not have a Shul in a room underneath a room where such symbols are found, and the Avnei Neizer (Shu”t Avnei Neizer, Orach Chaim No. 32) concurs, citing the story about Moshe from our parashah. The Kozhiglover Gaon, however (Shu”t Eretz Tzvi 1:31), is lenient, as is the Mishnah Berurah in the Sha’ar HaTziyun (Orach Chaim there No. 22). Rav Moshe Feinstein (Shu”t Igrot Moshe, Orach Chaim 1:47-48) discusses at some length the case of a Shul located immediately next to another religion’s house of worship (examining as well the situation if the Shul actually faces that other house); he rules that one may be lenient and daven in such a place, as the other religious symbols are not seen from the Shul and it is quite clear that the people in the Shul are davening to Hashem alone. See also the ruling of the Vilna Gaon as cited in Maaseh Rav (No. 47). It should be noted that according to the Aruch HaShulchan (Orach Chaim 154:1), this entire issue pertains only to an actual Shul established in a room beneath a place which contains other religious symbols, but an individual may certainly daven in a room which may be underneath such a place.