Reference for Zavim 1:6
רָאָה אַחַת הַיּוֹם וְאַחַת בֵּין הַשְּׁמָשׁוֹת, אַחַת בֵּין הַשְּׁמָשׁוֹת וְאַחַת לְמָחָר, אִם יָדוּעַ שֶׁמִּקְצָת הָרְאִיָּה מֵהַיּוֹם וּמִקְצָתָהּ לְמָחָר, וַדַּאי לַקָּרְבָּן וְלַטֻּמְאָה. אִם סָפֵק שֶׁמִּקְצָת הָרְאִיָּה מֵהַיּוֹם וּמִקְצָתָהּ לְמָחָר, וַדַּאי לַטֻּמְאָה וְסָפֵק לַקָּרְבָּן. רָאָה שְׁנֵי יָמִים בֵּין הַשְּׁמָשׁוֹת, סָפֵק לַטֻּמְאָה וְלַקָּרְבָּן. אַחַת בֵּין הַשְּׁמָשׁוֹת, סָפֵק לַטֻּמְאָה:
If he saw one [discharge] during the day and one at twilight, [or] one at twilight and one the next day, if it is known that part of the sighting [the discharge at twilight occurred] during the day and part was the next day, he is certain with regard to a sacrifice [that he must bring one as a <i>zav</i>] and with regard to uncleanliness [he is unclean]. If is was doubtful if part of the sighting was today and part was the next day, there is no doubt regarding his uncleanliness, but there is doubt regarding his sacrifice. If he saw [discharges] on two [consecutive] days at twilight, there is doubt regarding his uncleanliness and his sacrifice. If he saw one [discharge] at twilight, there is a doubt regarding his uncleanliness.