Gemara

29b (Mishnah): If he finds a bag, box or anything that normally he would not carry it, he leaves it there.

30a (Beraisa): We learn from "v'His'alamta" - sometimes you ignore an Aveidah, and sometimes not. If a Chacham sees an Aveidah that it is undignified for him to carry it, he ignores it.

30b (Rabah): If the Chacham hit the animal (so it will return to its owner), he is obligated to return it.

Abaye saw some goats. He threw a clod of earth at them.

Rabah: You are obligated to return them.

(Rava): Anything that a Chacham would take if it were his own, he must return if it belongs to another. If a Chacham would load or unload his own animal, he must help others load or unload.

R. Yishmael b'Rebbi Yosi saw a man carrying wood. The man rested, then asked R. Yishmael to help him load the wood. R. Yishmael bought the wood (to avoid needing to help), and made it Hefker. The man acquired the wood and asked for help; R. Yishmael again bought it and made it Hefker.

Question: (Loading) wood is below the honor of R. Yishmael b'Rebbi Yosi. He was exempt!

Answer: R. Yishmael b'Rebbi Yosi went beyond the letter of the law.

Rishonim

The Rif brings the Gemara.

Nimukei Yosef (DH Nischayav): Rashi and the Rambam say that once he started to return it, he must fully return it. According to this, the same applies to Kelim. The Ran was astounded, for Bava Basra says that one must fully return it only because it got used to straying! What bothered the Ran? Here (in Bava Metzia) we obligate full return even of Kelim that he would normally take in the field!

Rambam (Hilchos Gezeilah 11:13): If a dignified Chacham found a bag or box, and he does not normally carry such Kelim in his hand, he is not obligated to deal with it. He should evaluate: if he would take it back if it were his, he is obligated to return it to another. If he would not parfon his honor for his own, he is not obligated to return it.

Rambam (14): Similarly, if he found an animal and hit it, he is obligated to deal with it and return it, even though it is below his dignity, since he began the Mitzvah.

Rambam (17): One who goes in a straight path and goes beyond the letter of the law will return an Aveidah in every case, even if it is below his dignity.

Rosh (Bava Metzia 2:21): When the Torah exempted him, he should not disgrace his honor. It is forbidden to him, for he belittles the honor of Torah where there is no obligation. Even in a case of Safek (regarding an Aveidah it is not the field that he would not return in the city), he should not belittle a Safek Isur for the sake of Safek money of another. If a Chacham wants to go beyond the letter of the law, he will pardon his money (and pay the owner), like R. Yishmael b'Rebbi Yosi did. If the Chacham hit the animal, he is obligated to return it. He caused it to (move, and) find good pasture (and it is less likely to return home).

Poskim

Shulchan Aruch (CM 263:1): If a dignified Chacham found a bag or box, and he does not normally carry such Kelim in his hand, he is not obligated to deal with it.

Gra (1): The Gemara said 'Zaken'; this refers to a Chacham even if he is young, like we find with Abaye.

Note: He does not infer that Abaye was young because he threw earth at the goats, for if so, it was not below his dignity to take them! Rather, Rabah adopted Abaye, and Rabah died at 40.

Shulchan Aruch (ibid): He should evaluate: if he would take it back if it were his, he is obligated to return it to another. If he would not parfon his honor for his own, he is not obligated to return it.

Beis Yosef (DH ha'Motzei): Why did Rava need to say that anything that a Chacham would take if it were his own, he must return if it belongs to another? The Mishnah teaches this! The Rambam answers this. Rava teaches that he gauges if he would take his own Aveidah.

SMA (2 and Prishah 1 DH Im): He estimates: if his own was in a place prone to be stolen or get lost, if his concern for its loss would overcome his shame. I.e. even if he normally he would not carry this, but he would do so in order to avoid losing it, he is obligated.

Shulchan Aruch (2): Similarly, if he found an animal and hit it, he is obligated to deal with it and return it, even though it is below his dignity, since he began the Mitzvah.

Beis Yosef (DH v'Zeh): The Rambam says that one who started to return an animal must fully return it. This implies that this is only for an animal. He obligates one who found Kelim in the field to return them, for it is no disgrace to return them even in the city, but in a place where he would not normally return them, he can leave them even if he began. However, his reason was since he began the Mitzvah. This applies even to Kelim. This was the Ran's difficulty. The Rambam was not concerned for the proof from Bava Basra, for it was not said to explain, rather, to reject a proof. Alternatively, perhaps the Rambam obligates only for an animal. He means that once he began returning the animal, he must finish, for if not, he harmed the owner, for he accustomed it to straying. The continuation of the Rambam proves that this is correct. He obligates returning to a guarded place only regarding animals, then teaches that it is proper to go beyond the letter of the law and return even when it is below his dignity. The latter law does not belong here! Rather, he taught it here to teach that one must fully return animals because they learned to stray.

SMA (263:4): The Rambam holds that the Gemara discussed an animal to teach that even though he merely hit it and made it move, he must return it. Why did the Shulchan Aruch copy the words of the Rambam, which can be explained in two different ways (like the Beis Yosef explained)?!

Taz (DH v'Chen): The Rambam explains that in Bava Metzia, the Gemara's question was whether we say like the rejection in Bava Basra that the obligation (for one who started) applies only to animals! Since the Gemara did not decide, the Rambam concluded 'since he started' to show that this reason is primary. Once one became involved with the Aveidah he must return it, even if he did not begin to return it, like Abaye and the goats.

Shulchan Aruch (3): One who goes in a straight path and goes beyond the letter of the law will return an Aveidah in every case, even if it is below his dignity.

Beis Yosef (DH Kosav ha'Rambam): The Rambam learned from R. Yishmael b'Rebbi Yosi. The Tur omitted this because the Rosh disagreed. The Rambam holds that it honors Hash-m for a Chacham to go beyond the letter of the law and return, for another, something that he would not deal with if it were his own!

Rema: Some disagree and forbid, for it is below his dignity. If he wants to go beyond the letter of the law, he will pay from his own money.

Shulchan Aruch (28:5): If a Yisrael asked a Chacham to give monetary testimony for him in a Beis Din of smaller Chachamim than himself, he is not obligated to go.

R. Akiva Eiger (DH Eino): Anshei Keneses ha'Gedolah says that if he wants to pardon his honor and go, this is fine, for he can pardon his honor. This is like an Aveidah.