אורח חיים ע״חOrach Chayim 78

Se’if 1א׳

הָיָה קוֹרֵא, וְהִתְחִילוּ מֵי רַגְלָיו שׁוֹתְתִין עַל בִּרְכָּיו, פּוֹסֵק עַד שֶׁיִּכְלוּ הַמַּיִם, וְחוֹזֵר לִקְרוֹת, אֲפִלּוּ אִם נָפְלוּ עַל בְּגָדָיו וְיֵשׁ בָּהֶם טוֹפֵחַ עַל מְנַת לְהַטְפִּיחַ, כֵּיוָן שֶׁהֵם מְכֻסִים בְּבִגְדּוֹ. וְאִם נָפְלוּ מֵי רַגְלַיִם בָּאָרֶץ, מַרְחִיק מֵהֶם ד' אַמּוֹת: הַגָּה: אוֹ כְּשִׁעוּר שֶׁיִּתְבָּאֵר לְקַמָּן סִימָן פ"ב, אוֹ מַמְתִּין עַד שֶׁיִּבָּלְעוּ בַּקַּרְקַע. (הר"י (פ"ב) [פ"ג] דִּבְרָכוֹת) וַאֲפִלּוּ שָׁהָה כְּדֵי לִגְמֹר אֶת כֻּלָּהּ, אֵין צָרִיךְ לַחֲזֹר אֶלָּא לַמָּקוֹם שֶׁפָּסַק: הַגָּה: וְיֵשׁ אוֹמְרִים דְּאִם שָׁהָה כְּדֵי לִגְמֹר אֶת כֻּלָּהּ, חוֹזֵר לְרֹאשׁ. וְכֵן עִקָּר וּכְמוֹ שֶׁכָּתַבְתִּי לְעֵיל סי' ס"ה. וּמְשַׁעֲרִין לְפִי הַקּוֹרֵא:

One Who Needs to Urinate at the time of Recitation [of the Sh'ma], containing 1 Se'if If one was reciting, and urine began flowing onto their knees, they should pause until the flow stops, and [then] return to recite - even if it fell on his garments and it had [enough] moisture to moisten [a surface which could in turn moisten another surface], since it is covered by one's clothing (ie. he had another layer of dry clothing on top of the wet one) [they can continue to recite]. And if urine fell on the ground, one should distance from it 4 amot. Rem"a: Or [they should distance themselves] the amount that will be clarified below in Siman 82, or one can wait until it is absorbed into the ground [The Ri, Chapter 2 of B'rachot] And even if one delayed enough to finish all of it [i.e. the recitation], there is no need to go back [in the recitation] other than to the place that one paused. Rem"a: And there are those who say that if one delayed enough to finish all of it, they must return to the beginning, and this is the main [position that one should follow] like what I wrote above in Siman 65. And it is calculated according to the [time it would take the particular] reader.