Mishnah Taharos 6:4: However many uncertainties, and uncertainties upon uncertainties that you might increase, a case of uncertainty in a private domain is impure, and [an uncertainty] in a public domain is pure. How so? If one entered an alleyway and something impure was in the courtyard [which one enters into through the alleyway], and there is an uncertainty as to whether he entered [the courtyard] or did not enter; or if something impure was in a house and there is an uncertainty as to whether he entered or did not enter; or even if he entered, if there is an uncertainty as to whether it was there [i.e. whether the impure thing was in the house at the time that he entered] or was not there; or even if it was there, if there is an uncertainty as to whether it consisted of the [sufficient] amount [required in order for something to render one impure] or did not consist of the [sufficient] amount; or even if it did consist [of the sufficient amount], if there is an uncertainty as to whether it was something impure or pure; and even if it was something impure, if there is an uncertainty as to whether he touched it or not; [for any such case] its uncertainty is impure. Rabbi Elazar says: if there is an uncertainty as to whether one entered [into the impure courtyard or house], it is pure; but if there is an uncertainty as to whether one touched [something impure], it is impure.

כֹּל שֶׁאַתָּה יָכוֹל לְרַבּוֹת סְפֵקוֹת וּסְפֵק סְפֵקוֹת, בִּרְשׁוּת הַיָּחִיד, טָמֵא. בִּרְשׁוּת הָרַבִּים, טָהוֹר. כֵּיצַד, נִכְנַס לְמָבוֹי וְהַטֻּמְאָה בֶחָצֵר, סָפֵק נִכְנַס סָפֵק לֹא נִכְנַס, טֻמְאָה בַּבַּיִת, סָפֵק נִכְנַס סָפֵק לֹא נִכְנַס, וַאֲפִלּוּ נִכְנַס, סָפֵק הָיְתָה שָׁם סָפֵק לֹא הָיְתָה שָׁם, וַאֲפִלּוּ הָיְתָה שָׁם, סָפֵק שֶׁיֶּשׁ בָּהּ כַּשִּׁעוּר סָפֵק שֶׁאֵין בָּהּ כַּשִּׁעוּר, וַאֲפִלּוּ שֶׁיֶּשׁ בָּהּ, סָפֵק טֻמְאָה סָפֵק טָהֳרָה, וַאֲפִלּוּ טֻמְאָה, סָפֵק נָגַע סָפֵק לֹא נָגַע, סְפֵקוֹ טָמֵא. רַבִּי אֶלְעָזָר אוֹמֵר, סְפֵק בִּיאָה, טָהוֹר. סְפֵק מַגַּע טֻמְאָה, טָמֵא:

Mishnah Taharos 6:5: If one entered a valley during the rainy season, and there was something impure in a particular field and he said, "I walked to that place, but I do not know whether I entered that field or did not enter it, Rabbi Elazar declares him pure, but the Sages declare him impure.

נִכְנַס לְבִקְעָה בִּימוֹת הַגְּשָׁמִים, וְטֻמְאָה בְּשָׂדֶה פְלוֹנִית, וְאָמַר, הָלַכְתִּי לַמָּקוֹם הַלָּז וְאֵינִי יוֹדֵעַ אִם נִכְנַסְתִּי לְאוֹתוֹ הַשָּׂדֶה וְאִם לֹא נִכְנַסְתִּי, רַבִּי אֶלְעָזָר מְטַהֵר, וַחֲכָמִים מְטַמְּאִין: