Siman 78

We learn in Berakhot (22b): Our rabbis taught: If one was standing in prayer, and water was dripping upon his knees, meaning that he was urinating – he stops until the water ceases, and returns and prays. And if he did not tarry long enough to complete all of it – he returns to the place where he stopped. And if he tarried long enough to complete all of it – he returns to the beginning. And we have already explained in siman 65 that according to the Rif and the Rambam, we only hold thus regarding prayer, that he returns to the beginning. However, regarding the recitation of Shema, even if he tarried long enough to complete all of it – he does not return to the beginning. But the Tosafot and the Rosh disagree on this, and they hold that there is no difference between prayer and the recitation of Shema, and whenever the interruption was by necessity, such that he was unable to recite – he returns to the beginning even in the recitation of Shema. Our teacher, the Beit Yosef, ruled in his name like the Rif and the Rambam. The Tur and our teacher, the Rema, ruled like the Tosafot and the Rosh, see there.

And therefore the Tur wrote here: If one was reciting, and his urine began to flow upon his knees – he stops until the water ceases… and if he delayed long enough to finish the whole [recitation] – he returns to the beginning. And if not – he returns to the place where he stopped. Thus far his words. But our teacher, the Beit Yosef, wrote that even if he delayed long enough to finish the whole [recitation] – he only needs to return to the place where he stopped. Thus far his words. And our teacher, the Rema, wrote on this: And some say that if he delayed long enough to finish the whole [recitation] – he returns to the beginning. And such is the primary [ruling], and as I have written above in siman 65. And one estimates according to the [pace of the] reader. Thus far his words.

Regarding urine when it has flowed from him, if he is walking without trousers and they fell upon the ground – he must distance himself from them four amot or go out to another room, whether during the recitation of Shema or during the prayer. And even though one should not go from place to place in the middle of the prayer, nevertheless here it is necessarily so. And even though it is unavoidable that a small amount also fell upon his knees, nevertheless we are not concerned about this, even if his knees are still moist from the urine (Pri Megadim and Eliyah Zuta). And if the place is soft ground, which can absorb them quickly in a manner that there will not be enough moisture to moisten another object – he has the permission to wait until they are absorbed. And we are not concerned lest he linger in the waiting for a duration long enough to finish the entire prayer, and he would have to return to the beginning according to the opinion of the Tosafot and the Rosh. For what of it? For even if he recites it twice, this is only like one who reads from the Torah. Therefore, during the prayer he should not wait until they are absorbed, for perhaps he will linger a long time and will have to return to the beginning, and he will cause blessings that are not necessary. Therefore, during the prayer in any case he distances himself four amot and recites immediately. And also during the recitation of Shema it is better to do so. And certainly if he is standing during the blessings of the recitation of Shema, which is like the prayer, and he is obligated to distance himself four amot or go to another room. (See Magen Avraham subsection 2, and the matters are difficult. And it is better also during the recitation of Shema to distance oneself. And examine carefully and you will find it simple.)

And all this is when the urine did not fall upon his clothes. But if they fell upon his clothes, such as a tunic or trousers, and they have moisture sufficient to moisten another object, the law is as follows: if they are covered by clean clothes, for example, if the upper garment upon him is clean of the urine – he may recite thus, for even regarding excrement on one's clothes we hold that when it is covered we have no concern with it, as I wrote in siman 76, section 8. And all the more so regarding urine. But if they are not covered, for example, if he has no upper garment upon him, or if the upper one was also moistened by the urine – he must remove his clothes. And this is regarding Kiryat Shema. But regarding prayer, where it is impossible to interrupt so much to strip off his clothes – he may pray as he is even though they are revealed, since according to the Torah it is permitted as I wrote in the previous siman, and the prohibition is rabbinic. And regarding prayer they permitted it, since it is impossible otherwise (Beit Yosef and Magen Avraham, subsection 1).

One who has an illness, such that urine drips from him constantly against his will, and if so, he would never be able to pray, our teacher, the Rema, wrote in a responsum (siman 98) that it is permitted to make for him a garment around the organ. Consequently, the outer garments will be clean, and he will be able to go to the beit knesset to pray. At the time of the dripping, he shall pause and afterward pray. He may begin to pray when it is not a time of dripping, even though he knows he will need to pause, since it is impossible otherwise. See there.