Gemara

(R. Yehoshua ben Levi): In 24 verses, Kohanim are called Leviyim, e.g. "veha'Kohanim ha'Leviyim Bnei Tzadok."

Chulin 131a: A certain Levi used to seize Matanos (being sent to a Kohen).

Rav: Is it not enough that we do not make him give, that he even grabs from others?!

Question: (Matanos are taken "Me'es ha'Am.") If Rav holds that Leviyim are included in "ha'Am", we should take from Leviyim. If they are not included, why did Rav say "is it not enough that we do not make him give"? The Torah exempts him!

Answer: Rav is unsure whether they are included.

Tana'im argue about this;

(Beraisa #1): Avodas Yom Kipur atones for "Am ha'Kahal", i.e. Yisrael. "Yechaper" teaches about the Leviyim. (Leviyim are not included in "Am ha'Kahal");

(Beraisa #2): "Yechaper" teaches that it atones for slaves. (This Tana must hold that Leviyim are included in "ha'Kahal.")

Rav was unsure whom the Halachah follows.

(Mereimar): The Halachah follows Rav.

Bava Metzi'a 6b: A case occurred in which Reuven and Shimon were fighting over a bathhouse. Each said 'it is mine.' Reuven was Makdish it.

Question: May people benefit from it?

Answer (Rav Hamnuna - Mishnah): Regarding a Safek Bechor, ha'Motzi me'Chavero Alav ha'Re'ayah.

If a Kohen took a Safek Bechor, we do not force him to return it, for it says ha'Motzi me'Chavero Alav ha'Re'ayah. Even if he did not take it, a Beraisa teaches that one may not shear or work it!

Rejection (Rabah): Perhaps we force a Kohen who took a Safek Bechor to return it. A Safek Bechor is forbidden because Kedushas Bechor comes automatically. (However, one can be Makdish a bathhouse only if it is in his Reshus.)

Support (for Rabah - Rav Chananya - Beraisa): Sefek (Bechoros) are tithed with other animals.

If a Kohen who took a Safek may keep it, how could the Yisrael make it Ma'aser? He exempts his obligation with the Kohen's property!

Rejection (Abaye): A Safek is not tithed;

(Mishnah): If an animal already counted (during tithing) jumped back into the pen and was mixed with the uncounted animals, they are all exempt.

This shows that the Torah requires a definite "Asiri (tenth)".

(Rav Acha mi'Difti): The Beraisa cannot discuss Safek Bechoros. It says "(the tenth) will be Kodesh." If it is already Kodesh, it cannot become Ma'aser! Rather, they are animals designated to redeem Safek Bechor donkeys.

(Rav Nachman): If a Yisrael has 10 Safek Bechor donkeys, he sets aside 10 sheep or goats and tithes them. They all belong to him.

Rishonim

Hilchos Bikurim (9:8): Kohanim and Leviyim are exempt from Matanos, for it says "Me'es ha'Am." It is a Safek whether Leviyim are included in "ha'Am". Therefore, we do not take from them. If a Kohen took, he does not return it.

Rambam (Hilchos Bechoros 5:3): Any Bechor that is a Safek, it grazes until it gets a Mum (blemish) and the owner eats it. If a Kohen seized it, we do not take it from him.

Rambam (2:6): If a cow gave birth to the form of a horse or camel, which has no Kedushas Bechorah, even if it has some Simanim like a cow, it is a Safek Bechor. Therefore, the owner eats it. If a Kohen seized it, we do not take it from him.

Rashba (1:311): It seems that the Gemara concluded that we take it from him. Why did the Rambam write that we do not take it from him? In his defense, I say that he relied on Rav Hamnuna. If we would say that we take it from him (from the Kohen), why did the Mishnah say Stam ha'Motzi mi'Chavero Alav ha'Re'ayah? (This connotes that neither can take from the other without a proof.) The Gemara (Kesuvos 76b) asked like this (if the butcher needs a proof to take from the buyer, but not vice-versa, why does it say ha'Motzi mi'Chavero Alav ha'Re'ayah)? It needed to answer that Stam, the buyer does not pay until the seller gives the animal. Rabah gave a mere Dichuy (presumably indeed we do not take it from him, just it is possible to say that we take it from him). This is why he said 'I could say', and he did not say 'there, if a Kohen seized it...' I.e. the Isur of shearing and working with a Safek Bechor does not depend on whether we take it from the Kohen. Even though R. Chinena (our text - Rav Chananya) surely holds that we take it from him, we hold like Rav Hamnuna. Firstly, the Mishnah is like him. Also, whenever two Amora'im argue and the Halachah was not fixed like either of them, it is a Safek, and we do not we do not take from one who seized. Even though Rav Chinena brought a support from a Beraisa, Rav Hamnuna can say that a Kedushah that comes by itself is different. Even though there is a Mitzvah to be Mekadesh a Bechor, if he did not it is Kodesh (by itself). Therefore, it is an even Safek. Neither the Kohen or the Yisrael is more Muchzak than the other. Therefore, Kol d'Alim Gavar (whoever overpowers, he keeps it). The Yisrael is totally Muchzak in the Sefekos (of the Beraisa, i.e. Pidyonei Peter Chamor). The Kohen has no Kinyan in the donkey. If it will not be redeemed, it is killed. If it is redeemed, it belongs to the Yisrael. It is a Safek whether the Seh is in place of it. The Yisrael is Muchzak in the Seh. Therefore, if a Kohen seized it, we take it from him. Abaye concluded that there is no support for Rav Hamnuna, and no question against him. We can say so to defend the Rambam.

Ran (Chulin 45a DH v'Hilchesa): Since it is a Safek, if a Kohen seized it, we take it from him and return it to the Levi. In Bava Metzi'a we conclude that ha'Motzi mi'Chavero Alav ha'Re'ayah, even if the Kohen grabbed it. This is the law for anyone who seizes Safek Mamon (property). Why does the Rambam say that if a Kohen took Matanos from a Levi, he keeps it? Why is this different than a Safek Bechor?

Kesef Mishneh (Hilchos Bikurim 9:8): The Rambam (Hilchos Bechoros 5:3) holds that if a Kohen took a Safek Bechor, we do not take it from him!

Ran (ibid.): Whenever the giver has Tovas Hana'ah (the right to choose to whom to give it), if the Kohen seized it, he must return it. Even if he does not have Tovas Hana'ah, e.g. Leket, Shichchah and Pe'ah, he need not give to the first who claims it. If he did, why did the Gemara say Ein Lo Tov'im (no one can clam them) regarding Leket, Shichchah and Pe'ah? The first poor person to come can claim them! Rather, Ein Lo Tovas Hana'ah just means that if one took, we do not take it from him. Also Tosfos (131a DH Yesh) says so. Surely this is true according to the opinion that Tovas Hana'ah is Mamon (the right to choose to whom to give it is considered the giver's property). It follows that when one has Tovas Hana'ah, if one took, we take it from him. Since the owner of an animal has Tovas Hana'ah regarding Matanos, if a Kohen took from a Levi, he must return it. The Levi may keep it, for it is Safek Mamon.

Gra (YD 61:22): Tosfos did not distinguish (based on whether Tovas Hana'ah is Mamon). The Rambam rules like Tovas Hana'ah is not Mamon.

Kesef Mishneh (2:6): The Gemara did not resolve the case of a cow that gave birth to the form of a horse or camel, but has some Simanim like a cow. Therefore, the Rambam ruled that it is a Safek Bechor. He said that if a Kohen seized it, we do not take it from him. He learned from Rav Hamnuna. Why did the Rambam rule like him, unlike Rabah and Rav Chananya? He holds that Rabah is a mere Dichuy. Rav Chananya's support is not strong. Since it is in the Yisrael's Reshus, and ha'Motzi mi'Chavero Alav ha'Re'ayah, even though if a Kohen seized it we do not take it from him, he can exempt himself with it.

Tosfos (Bava Metzi'a 6b DH v'Ha): When a Kohen grabbed a Safek Bechor, why don't we take it from him? The owner can say 'I wanted to give it to another Kohen!' We can say that we discuss Makirei Kehunah (to always give Matanos Kehunah to this Kohen). Alternatively, the owner can claim from the Kohen only the Tovas Hana'ah that he had in it, according to the opinion that Tovas Hana'ah is Mamon. In Chulin, we say that the Levi who used to grab Matanos Kehunah was impudent. This connotes that he need not pay. There is no proof from there. Perhaps he ate them; one who damages Matanos Kehunah is exempt.

Poskim

Shulchan Aruch (YD 61:23): It is a Safek whether a Levi must give Matanos. Therefore, he is exempt. If the Kohen took from him, he need not return it.

Bach (17): Also the Rashba (Toras ha'Bayis 3:2, 69a) says that if a Kohen took from a Levi, he need not return them. The Ran and Ro'oh asked from a Safek Bechor. I say that there is different, for it is a Safek to everyone. (No one can say 'I know that it is a Bechor.') Here, it is a Safek which Tana we follow. The Kohen can say 'I am sure that the Halachah follows this Tana.' Why does the Rambam distinguish (from Safek Bechor)? I say that he learned from the Levi who used to grab Matanos. Rav was astounded at his audacity, but we do not find that Rav forced him to return them.

Shach (13): Why did the Bach question the Rambam? Also regarding Safek Bechor, the Rambam holds that we do not take it from the Kohen. He should have questioned the Tur, who rules (YD 315) that we take from him a Safek Bechor! The Bach's answer is wrong. It is clear from Bava Basra (105a) and Bava Metzi'a (102b) that it does not matter whether he can say 'I am sure.' Also the Rosh (Bava Metzi'a 1:13) equates them. Rather, regarding a Bechor, the Safek is in the very matter they argue about. Therefore, the Kohen must bring a proof in order to keep it. If not, we leave it in its Chazakah with the original owner. Most animals are not Bechoros. The Safek about whether Leviyim must give is not in the Matanos themselves. Then, the Kohen can say 'until you bring a proof, the Matanos are mine.' The Rashba and Ro'oh hold like this; I explained it more. Also the Rema (below) distinguishes like this. Here he says 'some disagree', and in Siman 315 he writes 'this is the Halachah.' Here the Levush brought only the Mechaber's opinion, and in 315 he wrote 'we take it from him.'

Pischei Teshuvah (9): Tif'eres l'Moshe (in Yalkut Meforshim in Shulchan Aruch ha'Shalem) says that here we discuss a Levi who did not know that he is exempt and let a Kohen take. Siman 315 discusses a Kohen who seized. The Tur obligates him to return, for the Yisrael has Tovas Hana'ah.

Rema: Some disagree, and say that we take it from him.

Levush (22): If a Yisrael gave Matanos to a Levi, this requires investigation whether we take them from him. It is a Safek whether the Yisrael fulfilled his Mitzvah to give to a Kohen. The Levi's Chazakah is a Safek; this is not a Chazakah. Or, perhaps the Levi can say 'I say that he was Yotzei. Ha'Motzi mi'Chavero Alav ha'Re'ayah.'

Shach (12): If a Levi took from a Yisrael, the Bach (above) says that we do not take from them (he learned from Rav's reaction). The Levush was unsure. I say that surely we take it from him. It says "Zeh Yihyeh Mishpat ha'Kohanim." Leviyim are not called Kohanim.

Bach (DH u'Mah she'Chasav v'Ein): The Tur teaches that the Levi can say 'I hold that Leviyim are not called Am' to exempt himself from giving, but not in order to give to Leviyim l'Chatchilah.