Reference for Chullin 6:2
הַשּׁוֹחֵט וְנִמְצָא טְרֵפָה, וְהַשּׁוֹחֵט לַעֲבוֹדָה זָרָה, וְהַשּׁוֹחֵט חֻלִּין בִּפְנִים, וְקָדָשִׁים בַּחוּץ, חַיָּה וָעוֹף הַנִּסְקָלִים, רַבִּי מֵאִיר מְחַיֵּב, וַחֲכָמִים פּוֹטְרִין. הַשׁוֹחֵט וְנִתְנַבְּלָה בְיָדוֹ, הַנּוֹחֵר, וְהַמְעַקֵּר, פָּטוּר מִלְּכַסּוֹת:
When an animal was slaughtered and found to be Terefá, or if it was slaughtered for idolatrous purposes, or as חולין within, or as consecrated offerings without the temple-court; or a bird or wild animal condemned to lapidation, R. Meir considers it obligatory [to cover the blood], but the sages hold, "It is not obligatory to do so." When it became Nebelah by being slaughtered, or when it was killed by a knife being thrust up its nostrils, or that the trachea and œsophagus were forcibly torn off, it is not obligatory to cover the blood.