Siman 85

It was taught in a baraita (24b): If one was walking in filthy alleyways—he may not recite Kriyat Shema. Furthermore, if he was in the middle of reciting—he must stop. And if he did not stop, regarding him the verse says: "Because he has despised the word of Hashem." And if he stopped, what is his reward? Regarding him the verse says, "And through this matter you shall prolong your days." And when he exits from there, he completes the Kriyat Shema. And even if he delayed for a duration sufficient to complete all of it, our teacher, the Beit Yosef, ruled that he only needs to return to the place where he stopped. This is the approach of the Rif and the Rambam, that only regarding prayer must one return to the beginning, as I wrote in siman 65. Our teacher, the Rema, wrote that there are those who say he returns to the beginning, according to the opinion of the Tosafot and the Rosh that was explained there.

Even to meditate on words of Torah is forbidden in filthy places, and in a bathhouse and in a latrine. And "a place of filth" refers to places where there is excrement or urine. And even the laws of the bathhouse are forbidden to meditate upon in the bathhouse, and likewise the laws of the latrine in the latrine. Therefore, one should think about his accounts there, so that he does not come to meditation (Magen Avraham). And mundane matters are permitted to be spoken there in the holy tongue, but it is a measure of piety to be stringent (ibid.). And likewise, the descriptive attributes such as "Merciful," "Faithful," and the like—it is permitted to say them there. But names that may not be erased—it is forbidden to mention or to meditate upon. And likewise, the giving of a greeting is forbidden there. And it has already been explained that to separate one from a prohibition is permitted even in the holy tongue and in holy matters. And likewise, if a meditation of lewdness enters his heart, it is permitted to meditate on words of Torah, for it is like separating from a prohibition (ibid.). And it has already been explained in siman 74 that facing lewdness, meditation is permitted (ibid.). And our teacher, the Rema, wrote that in a place where it is permitted to meditate on words of Torah, it is permitted to rule on a law, provided that he does not state the reason for the matter. Thus far his words. And when he does not speak in the language of a ruling, but rather says to him "do such and such for me"—it is permitted, even though a law may be learned from this (ibid.). And one who is naked—it is forbidden to hear a blessing from another, and it is forbidden for him to answer "Amen." And see in Yoreh Deah siman 1 (ibid.).