Pesachim 30
פסחים ל׳ — ד"ה אֵין טָשִׁין אֶת הַתַּנּוּר בְּאַלְיָה
Pesachim 30:2
Vessels that absorbed leavened bread only when cool may be used for matza, except for the leaven container (whose potent leavening penetrates even without heat) and the spice container with flour, which have the same stringent status.
אָמַר רָבָא בַּר אַבָּא אָמַר רַב חִיָּיא בַּר אָשֵׁי אָמַר שְׁמוּאֵל: כׇּל הַכֵּלִים שֶׁנִּשְׁתַּמְּשׁוּ בָּהֶן חָמֵץ בְּצוֹנֵן — מִשְׁתַּמֵּשׁ בָּהֶן מַצָּה, חוּץ מִן בֵּית שְׂאוֹר, הוֹאִיל שֶׁחִימּוּצוֹ קָשֶׁה. אָמַר רַב אָשֵׁי: וּבֵית חֲרוֹסֶת — כְּבֵית שְׂאוֹר שֶׁחִימּוּצוֹ קָשֶׁה דָּמֵי.
The Gemara continues discussing the ways that a vessel must be cleansed so that it can be used during Passover. Rava bar Abba said that Rav Ḥiyya bar Ashi said that Shmuel said: Any vessel that was used for leavened bread only while cool can be used for matza, because no flavor of the leavened bread was absorbed by the vessel. The exception to this rule is the leaven container where the yeast was stored, since its leavening is more potent, and it can be assumed that the flavor from the yeast has entered the walls of the vessel even without heat. Rav Ashi said: And the spice container, in which potent spices that contained flour were stored, has the same status as the leaven container whose leavening is potent.