Midrash for Berakhot 3:5
הָיָה עוֹמֵד בַּתְּפִלָּה, וְנִזְכַּר שֶׁהוּא בַעַל קְרִי, לֹא יַפְסִיק, אֶלָּא יְקַצֵּר. יָרַד לִטְבֹּל, אִם יָכוֹל לַעֲלוֹת וּלְהִתְכַּסּוֹת וְלִקְרוֹת עַד שֶׁלֹּא תָנֵץ הַחַמָּה, יַעֲלֶה וְיִתְכַּסֶּה וְיִקְרָא. וְאִם לָאו, יִתְכַּסֶּה בַמַּיִם וְיִקְרָא. אֲבָל לֹא יִתְכַּסֶּה, לֹא בַמַּיִם הָרָעִים וְלֹא בְמֵי הַמִּשְׁרָה, עַד שֶׁיַּטִּיל לְתוֹכָן מָיִם. וְכַמָּה יַרְחִיק מֵהֶם וּמִן הַצּוֹאָה, אַרְבַּע אַמּוֹת:
If in the middle of tefillah (shemoneh esreh) he remembered that he had experienced a seminal discharge, he should not break off [his prayer entirely], but he should shorten [each blessing]. If he had gone down to immerse himself — if he can come up, cover himself, and recite the Shema before sunrise, he should do so. [For the vatikin (the exceptionally pious) are exacting with themselves to conclude it at sunrise, it being written (Psalms 72:5): "They shall fear You with the sun."] And if not, he should cover himself with the water and recite it. [And only in clouded water, where his nakedness is not exposed, but not in clear water.] But he should not cover himself with bad [i.e., foul] water, or with steeping water [water in which flax is steeped], until he dilutes it. [There is something missing here. It is to be understood thus: "And he should not recite it near urine until he has diluted it." The amount of water for diluting a single urinal discharge is a revi'ith.] And how far should one remove himself from it [from undiluted urine] and from feces" Four ells. [And only when it is to the side of him or behind him; but if it is in front of him, he must remove himself until it is out of sight.]