Zevachim 96A

אלא קדירות של מקדש, אמאי אמר רחמנא ישברו? נהדרינהו לכבשונות! אמר רבי זירא: לפי שאין עושין כבשונות בירושלים.

The Talmud challenges: But according to the opinion that earthenware vessels can be cleansed of their absorbed substances by the process of kindling, with regard to pots used in the Temple, why does God state in the Torah that they should be broken? Let us simply return them to the kilns in which pots are made to be sure that the pots will be cleansed by the extreme heat of the kilns. R' Zeira said: The pots cannot be returned to kilns because, as taught in a baraita (see Bava Kamma 82b), kilns are not built in Jerusalem because of the great quantity of smoke they produce.

אמר אביי: וכי עושין אשפתות בעזרה?! אישתמיטתיה הא דתני שמעיה בקלנבו: שברי כלי חרס נבלעין במקומן.

The Talmud presents an objection to R' Zeira’s answer. Abaye said: But if, as the baraita teaches, there are no kilns in Jerusalem, are scrap heaps of earthenware assembled in the Temple courtyard? The same baraita also teaches that there are no scrap heaps in Jerusalem. What, then, is done with the shards of earthenware vessels that must be broken in the courtyard? The Talmud dismisses the question: Abaye raised that objection only because that which Shemaya taught in Kalnevo escaped him; Shemaya taught there: In the Temple, shards of earthenware vessels were miraculously absorbed in their place.

אלא הא דאמר רב נחמן אמר רבה בר אבוה: תנור של מקדש של מתכת הוה ⁠– נעביד דחרס, דהסיקו מבפנים הוא!

The Talmud returns to the topic of kindling earthenware vessels and asks: But if kindling from within cleanses everything absorbed in an earthenware oven, what is the reason for that which Rav Naḥman says that Rabba bar Avuh says: The oven in the Temple was fashioned of metal? Let us fashion it of earthenware, as an oven’s kindling is from the inside, and, accordingly, it would be possible to cleanse it?