Bekhorot 49B

הכא נמי לא שנא.

Here, too, the halakha is no different.

ושמואל אמר לך: התם ⁠— בידו לקדשה מעכשיו, הכא ⁠— אין בידו לפדותו מעכשיו. ואף על גב דקיימא לן, דכל היכא דפליגי רב ושמואל ⁠— הלכתא כרב באיסורי וכשמואל בדיני, הכא הלכתא כוותיה דשמואל.

And Shmuel could say to you: There, with regard to betrothal, it is in his power to betroth her from now, when he gave her the coins, and therefore it is irrelevant that the money was spent. Conversely, here, in the case of redemption, it is not in his power to redeem his son from now. With regard to the practical halakha in this dispute the Talmud comments: And even though we maintain as a principle that wherever Rav and Shmuel disagree the halakha is in accordance with the opinion of Rav in ritual matters and in accordance with the opinion of Shmuel in monetary matters, here the halakha is in accordance with the opinion of Shmuel, who holds that if one redeems his son within 30 days he is not redeemed.

תנן: מת בתוך שלשים יום, אף על פי שנתן לכהן ⁠— יחזיר לו חמש סלעים. טעמא דמת, הא לא מת ⁠— בנו פדוי! הכא במאי עסקינן? דאיתנהו למעות.

The Talmud raises a difficulty: We learned in the Mishnah on the previous amud: If the firstborn son dies within 30 days of birth, although the father gave 5 sela coins to the priest, the priest must return the 5 sela coins to him. The Talmud infers: The reason he must return the money is that the son died. But if he did not die within 30 days his son is redeemed despite the fact that the father gave the priest the money prior to the proper time. This inference contradicts the opinion of Shmuel. The Talmud answers: Here we are dealing with a case where the money is still extant, i.e., in the priest’s possession.