Yoreh Deah Siman 24 Seif 14

 

יד כָּל אֵלּוּ הַחִלוּקִים כְּשֶׁהוּא וַדַּאי שֶׁלֹּא נָגַע בַּוֵּשֶׁט אֶלָּא בַּקָּנֶה לְצַד מַעְלָה; אֲבָל בַּוֵּשֶׁט, אֲפִלּוּ שָׁחַט בּוֹ כָּל שֶׁהוּא חוּץ לִמְקוֹם שְׁחִיטָה, בֵּין לְצַד מַעְלָה בֵּין לְצַד מַטָּה; וְכֵן בַּקָּנֶה לְצַד מַטָּה, קֹדֶם גְּמַר הֶכְשֵׁר שְׁחִיטָה, אַף עַל פִּי שֶׁגָּמַר כָּל הַשְּׁאָר בִּמְקוֹם שְׁחִיטָה, הֲרֵי זוֹ פְּסוּלָה, מִפְּנֵי שֶׁנְּקִיבַת מְקוֹמוֹת הַלָּלוּ בְּמַשֶּׁהוּ .

Seif 14

 

All of these sections [that which has just been discussed], when he is certain that he did not strike the gullet but rather only the windpipe [moving] upward. But even if you slaughter the gullet with the slightest cut outside the place permitted for slaughter, be it from the upper side or the lower side; or similarly with the windpipe from the side below before he finishes it in a kosher slaughter even if he finish [cutting] all of the remainder in a place permitted for kosher slaughter, it is not acceptable since even the smallest of these perforations count.