בכורות ג׳Bekhorot 3

Mishnah 1א׳

הַלּוֹקֵחַ בְּהֵמָה מִן הַנָּכְרִי וְאֵין יָדוּעַ אִם בִּכְּרָה וְאִם לֹא בִכְּרָה, רַבִּי יִשְׁמָעֵאל אוֹמֵר, עֵז בַּת שְׁנָתָהּ וַדַּאי לַכֹּהֵן, מִכָּאן וְאֵילָךְ סָפֵק. רָחֵל בַּת שְׁתַּיִם וַדַּאי לַכֹּהֵן, מִכָּאן וְאֵילָךְ סָפֵק. פָּרָה וַחֲמוֹר בְּנוֹת שָׁלשׁ וַדַּאי לַכֹּהֵן, מִכָּאן וְאֵילָךְ סָפֵק. אָמַר לוֹ רַבִּי עֲקִיבָא, אִלּוּ בַּוָּלָד בִּלְבַד בְּהֵמָה נִפְטֶרֶת, הָיָה כִדְבָרֶיךָ, אֶלָּא אָמְרוּ, סִימַן הַוָּלָד בִּבְהֵמָה דַקָּה, טִנוּף. וּבְגַסָּה, שִׁלְיָא. וּבְאִשָּׁה, שְׁפִיר וְשִׁלְיָא. זֶה הַכְּלָל, כֹּל שֶׁיָדוּעַ שֶׁבִּכְּרָה, אֵין כָּאן לַכֹּהֵן כְּלוּם. וְכֹל שֶׁלֹּא בִכְּרָה, הֲרֵי זֶה לַכֹּהֵן. אִם סָפֵק, יֵאָכֵל בְּמוּמוֹ לַבְּעָלִים. רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב אוֹמֵר, בְּהֵמָה גַסָּה שֶׁשָּׁפְעָה חֲרָרַת דָּם, הֲרֵי זוֹ תִקָּבֵר, וְנִפְטְרָה מִן הַבְּכוֹרָה:

If one buys an animal from a non-Jew and it is not known whether it had given birth or had not given birth, Rabbi Yishma'el says: [The offspring of] a goat in its first year certainly belongs to the priest. From that point on it is questionable. [The offspring of] a two-year-old ewe certainly belongs to the priest. From that point on it is questionable. [The offspring] of a three-year-old cow or donkey certainly belongs to the priest. From that point on it is questionable. Rabbi Akiva said to him: If an animal were exempted only with the birth of offspring, you would be correct. Rather they said: The sign of offspring in small cattle is filth [from the womb]. In large cattle [the sign is] the after-birth. In a woman [the sign is] the fetus and the after-birth. This is the general rule: When it is known that [the animal] has given birth, the priest receives nothing. When it has never given birth, it belongs to the priest. If there is a doubt, it is eaten blemished by the owners. Rabbi Eli'ezer ben Jacob says: If a large domestic animal discharges a clot of blood, [the clot] is buried, and [the mother] is exempt from [the obligations of] the firstborn.

Mishnah 2ב׳

רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר, הַלּוֹקֵחַ בְּהֵמָה מְנִיקָה מִן הַנָּכְרִי, אֵינוֹ חוֹשֵׁשׁ שֶׁמָּא בְנָהּ שֶׁל אַחֶרֶת הָיָה. נִכְנַס לְתוֹךְ עֶדְרוֹ וְרָאָה אֶת הַמַּבְכִּירוֹת מְנִיקוֹת וְאֶת שֶׁאֵינָן מַבְכִּירוֹת מְנִיקוֹת, אֵינוֹ חוֹשֵׁשׁ שֶׁמָּא בְנָהּ שֶׁל זוֹ בָּא לוֹ אֵצֶל זוֹ, אוֹ שֶׁמָּא בְנָהּ שֶׁל זוֹ בָּא לוֹ אֵצֶל זוֹ:

Rabban Shim'on Ben Gamliel says: One who buys an animal that is nursing from a non-Jew need not be concerned that it had another child beforehand. If one entered his pen and saw those who had previously given birth nursing and those that had not previously given birth nursing, he need not be concerned that the child of this mother is nursing from that mother or that the child of that mother is nursing from this mother.