"To a pure place" -- that its place should be pure, and if it was impure he shall purify it. That a place should be prepared for them for this purpose. "To where the ashes are poured out" -- that there should be ashes there; that he should put the ashes there first; that there they should place the ashes. Rabbi Eliezer ben Yaakov says: that its place should be sloping. "And he shall burn it" -- one that is fit and not one that is unfit. "Upon wood in the fire" -- what does the text teach? For one might think, since burning is stated inside and burning is stated outside, just as the burning stated inside is with wood fit for the arrangement on the altar, so too the burning stated outside is with wood fit for the arrangement; the text says "upon wood" -- to include anything at all, even straw or stubble or brushwood. "In the fire" -- and not in lime and not in embers. "It shall be burned" -- even though there are no ashes there. "It shall be burned" -- even though one kindles the fire on its own body.
Burned in a Pure Place Where the Ashes Are Poured
Yalkut Shimoni on Torah 469:14
אֶל מָקוֹם טָהוֹר, שֶׁיְּהֵא מְקוֹמוֹ טָהוֹר וְאִם טָמֵא יְטַהֲרֶנּוּ. שֶׁיְּהֵא מָקוֹם מְתֻקָּן לָהֶם לְכָךְ. אֶל שֶׁפֶךְ הַדֶּשֶׁן, שֶׁיְּהֵא שָׁם דֶּשֶׁן, שֶׁיַּקְדִּים אֶת הַדֶּשֶׁן, שֶׁשָּׁם יְהוּ נוֹתְנִין אֶת הַדֶּשֶׁן. רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב אוֹמֵר, שֶׁיְּהֵא מְקוֹמוֹ מְשֻׁפָּךְ. וְשָׂרַף אֹתוֹ, כָּשֵׁר וְלֹא פָּסוּל. עַל עֵצִים בָּאֵשׁ, מַה תַּלְמוּד לוֹמַר, שֶׁיָּכוֹל הוֹאִיל וְנֶאֱמַר שְׂרֵפָה בִּפְנִים, וְנֶאֱמַר שְׂרֵפָה בַּחוּץ, מַה שְּׂרֵפָה הָאֲמוּרָה בִּפְנִים בְּעֵצִים כְּשֵׁרִים לְמַעֲרָכָה, אַף שְׂרֵפָה הָאֲמוּרָה בַּחוּץ בְּעֵצִים כְּשֵׁרִים לְמַעֲרָכָה, תַּלְמוּד לוֹמַר "עַל עֵצִים", לְרַבּוֹת כָּל מַשְׁמַע אֲפִלּוּ תֶּבֶן אוֹ בְּקַשׁ אוֹ בִּגְבָבָא. בָּאֵשׁ, וְלֹא בְּסִיד וְלֹא בְּרֶמֶץ. יִשָּׂרֵף, אַף עַל פִּי שֶׁאֵין שָׁם דֶּשֶׁן. יִשָּׂרֵף, אַל עַל פִּי שֶׁמַּצִּית אֶת הָאוּר בְּגוּפוֹ.