Arakhin 5B

ולרבי מאיר למאי איצטריך?

The Talmud asks: And as Rav stated his halakha in accordance with R' Meir, who says that one who valuates a child less than a month old must pay his assessment, for what reason was it necessary for Rav to state his ruling? Isn’t this obvious?

מהו דתימא: טעמא דרבי מאיר התם, דגזר פחות מבן חודש אטו בן חודש, אבל הכא דליכא למיגזר ⁠— אימא לא. קא משמע לן: טעמא דרבי מאיר דאין אדם מוציא דבריו לבטלה, לא שנא הכא ולא שנא הכא.

The Talmud answers: It was necessary for him to state this halakha, lest you say that the reason that R' Meir obligates him to pay the assessment there, in the case of the child, is that he decrees one must pay if the child is less than a month old, due to concern that otherwise people might mistakenly refrain from paying the valuation of a child who is a month old. But here, in the case of one who valuates a utensil, where there is no cause for such an error and therefore no need to decree, one might say that R' Meir would not obligate him to pay. Therefore, Rav teaches us that since the reason of R' Meir is that a person does not make his statement of consecration for naught, there is no difference between here, the case of a child, and there, with regard to a utensil. Rather, the halakha is the same in both cases.

כמאן אזלא הא דאמר רבה בר יוסף אמר רב, ואמרי לה אמר רב ייבא בר יוסי אמר רב: המקדיש בהמת חבירו נותן דמיה? כמאן ⁠— כרבי מאיר.

The Talmud asks: In accordance with whose opinion is that which Rabba bar Yosef says that Rav says, and some say that Rav Yeiva bar Yosei says that Rav says: One who consecrates the animal of another must give its assessment. In accordance with whom? It is in accordance with the opinion of R' Meir, that one does not issue a statement of consecration for naught. Since he knows that he cannot consecrate that which is not his, he meant to obligate himself in the animal’s assessment.