Reference for Zevachim 12:6
הָיוּ סוֹבְלִין אוֹתָם בְּמוֹטוֹת. יָצְאוּ הָרִאשׁוֹנִים חוּץ לְחוֹמַת הָעֲזָרָה וְהָאַחֲרוֹנִים לֹא יָצְאוּ, הָרִאשׁוֹנִים מְטַמְּאִין בְּגָדִים, וְהָאַחֲרוֹנִים אֵינָן מְטַמְּאִין בְּגָדִים, עַד שֶׁיֵּצֵאוּ. יָצְאוּ אֵלּוּ וָאֵלּוּ, אֵלּוּ וָאֵלּוּ מְטַמְּאִין בְּגָדִים. רַבִּי שִׁמְעוֹן אוֹמֵר, אֵלּוּ וָאֵלּוּ אֵינָן מְטַמְּאִין בְּגָדִים, עַד שֶׁיִּצַּת הָאוּר בְּרֻבָּן. נִתַּךְ הַבָּשָׂר, אֵין הַשּׂוֹרֵף מְטַמֵּא בְגָדִים:
They would carry the [bulls and goats] out on poles. Once the first ones [the men in front] pass the walls of the courtyard and the rear ones have not [yet] passed [the walls of the courtyard], the clothes of first ones become impure, but the clothes of the rear ones do not become impure until they have left. Once both sets have left, the clothing of both sets becomes impure. Rabbi Shimon says: Their clothes only become impure once the fire has burned most of the [offerings'] flesh. [Once] the flesh is charred, the clothing of someone [else] who burns [the flesh] does not become impure.