Avodah Zarah 76A

בת יומא, דלאו נותן טעם לפגם הוא.

that was used for cooking that same day by a non-Jew, as in such a case, it does not impart flavor to food cooked in it to the detriment of the mixture.

מכאן ואילך לישתרי! גזירה קדירה שאינה בת יומא משום קדירה בת יומא.

The Talmud asks: If so, from that point onward the pot should be permitted, as on the following day the taste of the non-kosher food imparted by the pot is already to the detriment of the food. The Talmud answers: There is a rabbinic decree that prohibits use of a pot that was not used by a non-Jew that same day, due to concern that one will use a pot used by a non-Jew that same day.

ואידך? קדירה בת יומא נמי מפגם פגמה.

The Talmud comments: And according to the opinion of the other tanna, who holds that even if the imparted flavor is to the detriment of the permitted food nevertheless it is forbidden, even the flavor imparted by a pot that was used that same day is detrimental to the flavor of the food, and still the Torah deems it forbidden, which proves that if a forbidden substance imparts flavor to a permitted food to its detriment, the permitted food is forbidden.

רמי ליה רב עמרם לרב ששת, תנן: השפודין והאסכלא ⁠— מלבנן באור, והתניא גבי קדשים: השפוד והאסכלא ⁠— מגעילן בחמין!

§ Rav Amram raises a contradiction before Rav Sheshet: We learned in the Mishnah: With regard to the spits and the grill, one must heat them until white-hot in the fire. But it is taught in a Mishnah (Zevaḥim 97a) with regard to sacrificial meat: The spit and the grill that were used to roast sacrificial meat may not be used again after the time for eating that particular offering has passed, as the leftover taste of the offering in these utensils is forbidden, unless one purges them in hot water. Apparently, heating them until white-hot is unnecessary.