Reference for Chullin 2:4
שָׁחַט אֶת הַוֶּשֶׁט וּפָסַק אֶת הַגַּרְגֶּרֶת, אוֹ שָׁחַט אֶת הַגַּרְגֶּרֶת וּפָסַק אֶת הַוֶּשֶׁט, אוֹ שֶׁשָּׁחַט אַחַד מֵהֶן וְהִמְתִּין לָהּ עַד שֶׁמֵּתָה, אוֹ שֶׁהֶחֱלִיד אֶת הַסַּכִּין תַּחַת הַשֵּׁנִי וּפְסָקוֹ, רַבִּי יְשֵׁבָב אוֹמֵר, נְבֵלָה. רַבִּי עֲקִיבָא אוֹמֵר, טְרֵפָה. כְּלָל אָמַר רַבִּי יְשֵׁבָב מִשּׁוּם רַבִּי יְהוֹשֻׁעַ, כֹּל שֶׁנִּפְסְלָה בִשְׁחִיטָתָהּ, נְבֵלָה. כֹּל שֶׁשְּׁחִיטָתָהּ כָּרָאוּי וְדָבָר אַחֵר גָּרַם לָהּ לִפָּסֵל, טְרֵפָה. וְהוֹדָה לוֹ רַבִּי עֲקִיבָא:
When the œsophagus had been duly cut through, but the trachea was torn off, or the reverse; or, that he cut through one of the tubes, and then waited till the animal died; or, that he covered or hid the knife by placing it under the second tube, and cut it off; it must, according to R. Jishbab, he considered as Nebelah [i.e. as an animal which died of itself], but, according to R. Akivah, as Terefá [i.e. an animal torn by wild beasts]. R. Jishbab gave the following rule from the authority of R. Joshua, "Every animal which, owing to a defect in slaughtering, has become Pasool [or unfit for use], must be considered as Nebelah; but when the slaughtering was duly performed, and it became Pasool through another cause, it must be considered as Terefá." Then R. Akivah assented to him [R. Jishbab].