46b
The gemoro tries to find how do we know that the fathers keeps the kesef kiddushin, maybe the girl keeps it herself.
The gemoro tries to bring a proof from es biti nosati leish hazeh. If the father marries her off, then obviously the father keeps the money. But the gemoro argues, maybe that's davka a ketanoh, but a naaroh marries herself off.
So how can the gemoro in the next proof, try to say, that we should learn that he keeps the money from boshes and pegam. The gemoro says in 40b that the father only gets the boshes and pegam because he can marry her off. But our gemoro is discussing a naaroh, whom we assume the father cannot marry her off, because if the father could marry her off, then obviously he keeps the kesef kiddushin??!
Avrumi Hersh, London england
1) Tosfos in Kidushin 3b (DH v'Chi) writes that the father can marry her off when she is a Na'arah and when he marries her off he gets the Kidushin money.
2) The Ramban in Kidushin 3b (DH v'Chi Teima) explains the aforementioned opinion in Tosfos that maintains that the father may marry off his daughter when she is a Na'arah. (The Ramban cites this in the name of "v'Yesh me'Raboseinu ha'Tzorfasim".) He writes that Tosfos derived this from the verse, "Es Biti Nasati," which includes all Nesinos and implies that the father can give her over for anything; he can even hand her over for Chupah.
The source for this is Rashi in Kesuvos 47a (DH Ha d'Zaki). The Gemara (47a) states that the Torah gives the Zechus to the father to hand his daughter over for Chupah. Rashi writes that this right is derived from "Es Biti Nasati," which implies all Nesinos. The Ramban writes that it is impossible to say that he handed her over when she was a Ketanah, because if so she would receive the punishment of Chenek if she was Mezanah, which does not fit with what the Torah states (Devarim 22:21) that if the Na'arah was Mezanah she gets Sekilah. The fact that she receives Sekilah proves that the father married her off when she was a Na'arah. This proves that the father may marry off his daughter when she is a Na'arah.
3) Here are further sources that the father may marry off his Na'arah daughter and he keeps the Kidushin money:
a) The simple reading in Rashi in the Mishnah here is that the father may marry off his daughter and keep the money. Rashi begins by writing that when the Mishnah states that the father is Zocheh in his daughter for Kidushin by money, this refers both to a Ketanah and to a Na'arah. The next Rashi says that the money belongs to him.
b) The first comment of the Shitah Mekubetzes on 46b says that the reason that the Mishnah writes "b'Kidusheha b'Kesef" is to tell us that even a Na'arah, who receives her Kidushin money herself, still has to give it to her father.
c) Rashi in Kidushin 3b (DH Zakai) writes that the money belongs to the father. He may hand her over for Bi'ah against her will while she is still a Na'arah.
d) The Rashba (Kidushin 3b, DH v'Su) writes that when the Gemara there asks, "How do we know that she is acquired through money and that the father gets the money," the question of the Gemara refers only to a Na'arah, because it is obvious that this applies to a Ketanah since he may even sell her. We know that the Mishnah -- which states that the father has a Zechus in his daughter -- is referring to a Na'arah because the Mishnah later (Kidushin 41a) states that a man may marry off his daughter when she is a Na'arah.
Dovid Bloom