Shabbos3: 2
תַּנּוּר שֶׁהִסִּיקוּהוּ בְקַשׁ וּבִגְבָבָא, לֹא יִתֵּן בֵּין מִתּוֹכוֹ בֵּין מֵעַל גַּבָּיו. כּוּפָּח שֶׁהִסִּיקוּהוּ בְקַשׁ וּבִגְבָבָא, הֲרֵי זֶה כְּכִירַיִם; בְּגֶפֶת וּבְעֵצִים, הֲרֵי הוּא כְתַּנוּר.
An oven that was heated with straw or with stubble, one may neither place [food] in it nor on it. A single stove that was heated with straw or with stubble is like a double stove; with marc or with wood, it is like an oven.