Zevachim 105B

מחוסר קריבה לאו כמחוסר מעשה דמי.

Even if the carcass of a kosher bird has not yet been brought close to being swallowed, it is still not considered as if a necessary action has not yet been performed, and an olive-bulk is sufficient to transmit impurity to food and drink.

איתיביה: שלשה עשר דברים נאמרו בנבלת עוף טהור, וזה אחד מהן: צריכה מחשבה, ואין צריכה הכשר, ומטמא טומאת אוכלין בכביצה. מאי, לאו רבי מאיר היא?

R' Ḥiyya bar Abba raised an objection to R' Abba bar Shmuel, based on a Mishnah (Teharot 1:1): 13 matters were stated with regard to the carcass of a kosher bird, and this is one of them: In order to be susceptible to impurity as a food, it requires a person’s intention that it be eaten; and it does not need to be rendered susceptible to such impurity by contact with liquid; and it transmits ritual impurity of food in the amount of an egg-bulk. In accordance with whose opinion is this Mishnah? What, is it not the opinion of R' Meir? If so, he holds that an egg-bulk of a carcass of a kosher bird is necessary to transmit impurity.

לא, רבנן היא.

The Talmud responds: No, the Mishnah is the opinion of the Rabbis.

והא קתני רישא: צריכה מחשבה ואין צריכה הכשר; ומאן שמעת ליה האי סברא ⁠– רבי מאיר; ומדרישא רבי מאיר, סיפא נמי רבי מאיר!

The Talmud challenges: But the first clause of that Mishnah teaches: In order to be susceptible to impurity as a food, it requires a person’s intention that it be eaten and it does not need to be rendered susceptible by contact with liquid. And from whom do you learn this reasoning? From R' Meir, as was taught in the baraita (105a). And since the first clause is the opinion of R' Meir, it follows that the latter clause is also the opinion of R' Meir.