יורה דעה שי״דYoreh De'ah 314

Se’if 1א׳

הַכֹּהֲנִים חֲשׁוּדִים לְהַטִּיל מוּם בִּבְכוֹר. אֲפִלּוּ אִם הוּא חָכָם וְיוֹשֵׁב בִּישִׁיבָה, אִם עָשָׂה דָּבָר שֶׁנִּרְאֶה כְּמַעֲרִים, כְּגוֹן שֶׁנָּתַן לִבְכוֹר שְׂעוֹרִים בְּסַל בְּעִנְיָן שֶׁכְּשֶׁיָּבֹא לְאָכְלָם נִפְגָּם שְׂפָתוֹ אוֹ כַּיּוֹצֵא בָּזֶה, אֵין לְשָׁחֲטוֹ עַל אוֹתוֹ הַמּוּם. וּלְפִיכָךְ כָּל מוּם שֶׁרָאוּי לְבֹא בִּידֵי אָדָם, אֵין שׁוֹחֲטִין אוֹתוֹ עָלָיו, עַד שֶׁיָּעִידוּ שֶׁמֵּעַצְמוֹ נָפַל בּוֹ. (טוּר).

Priests are suspected of putting a blemish in a firstborn. Even if he is a sage and sits in the academy, if he did a thing that looks like scheming — such as that he gave the firstborn barley in a wicker basket in such a way that, when it comes to eat it, its lip is split, or the like — one may not slaughter it on account of that blemish. And therefore any blemish that could come about by the hand of man, one does not slaughter it on account of it until they testify that it fell in it of itself (Tur).

Se’if 2ב׳

כָּל הַמּוּמִין הָרְאוּיִם לָבוֹא בִּידֵי אָדָם, נֶאֱמָן הָרוֹעֶה עֲלֵיהֶם לוֹמַר: מֵאֲלֵיהֶם נָפְלוּ וְלֹא נַעֲשׂוּ בְּכַוָּנָה, וְיִשְׁחַט עֲלֵיהֶם. בַּמֶּה דְּבָרִים אֲמוּרִים, כְּשֶׁהָיָה הָרוֹעֶה יִשְׂרָאֵל וְהַבְּכוֹר בְּיַד הַכֹּהֵן; אֲבָל אִם הָיָה הָרוֹעֶה כֹּהֵן וְהַבְּכוֹר עֲדַיִן הוּא בְּיַד בְּעָלָיו הַיִּשְׂרָאֵל, הֲרֵי זֶה אֵינוֹ נֶאֱמָן, וְחוֹשְׁדִין אוֹתוֹ שֶׁמָּא הוּא הִטִּיל בּוֹ כְּדֵי שֶׁיִּתְּנֶנּוּ לוֹ. וְיֵשׁ אוֹמְרִים דְּרוֹעֶה כֹּהֵן נֶאֱמָן עַל בְּכוֹר שֶׁל יִשְׂרָאֵל, וְיֵשׁ לְהָקֵל (טוּר בְּשֵׁם הָרֹא"שׁ וְהָרַמְבַּ"ן).

All the blemishes that could come about by the hand of man — the shepherd is believed concerning them to say: they fell of themselves and were not made deliberately; and it is slaughtered on account of them. When is this said? Where the shepherd was an Israelite and the firstborn was in the hand of the priest. But if the shepherd was a priest and the firstborn is still in the hand of its owner, the Israelite, he is not believed, and they suspect him lest he put it in it so that the owner should give it to him. And some say that a shepherd who is a priest is believed concerning the firstborn of an Israelite, and one may be lenient (Tur in the name of the Rosh and the Ramban).

Se’if 3ג׳

כֹּהֵן שֶׁהֵעִיד לְכֹהֵן אַחֵר שֶׁמּוּם זֶה מֵאֵלָיו נָפַל, נֶאֱמָן, וְאֵין חוֹשְׁשִׁין לָהֶם שֶׁמָּא הֵם גּוֹמְלִים זֶה אֶת זֶה.

A priest who testified for another priest that this blemish fell of itself is believed, and we are not concerned about them lest they are requiting one favour with another.