Gemara

103a (Mishnah): If Reuven stole a Perutah from Shimon and swore to deny it, Reuven must bring it to him even if Shimon is in Madai (overseas). He need not bring it if Shimon pardoned all but less than a Perutah of the principal.

103b - Inference: He must bring it to him only if he swore to deny it.

Suggestion: This is like R. Akiva. He obligates paying every one only if he swore falsely, for it says "la'Asher Hu Lo Yitnenu b'Yom Ashmaso."

Objection (Rav Huna bar Yehudah - Beraisa - R. Shimon ben Elazar): All agree that if one does not know from which person he bought, he may leave what he owes in front of them. R. Akiva and R. Tarfon argue about one who does not know from which one person he stole.

If he swore, the same should apply even when he bought!

(Rava): Since he knows from whom he stole and admitted to him and could return the money, it is as if Shimon said 'the theft is like a deposit with you.' Reuven must bring it to him only if he swore (and must bring an Asham).

105a - Version #1 (Rav Papa): If Shimon pardoned all except for less than a Perutah, Reuven need not go to return it, i.e. if the theft is not intact. If it is intact, he must return it, lest its value rise to a Perutah.

Version #2 (Rav Papa): Even if it is intact, we are not concerned lest it rise in value to a Perutah.

Rishonim

The Rif brings our Mishnah.

Rambam (Hilchos Gezeilah 7:9): If Reuven stole a Perutah from Shimon, even if he denied it, since he did not swear, if he admits he need not pursue Shimon to return it. Rather, he holds it until Shimon comes to take it. If he swore, he must pursue Shimon until he returns it, even if Shimon is in an island in the ocean, for once he swore Shimon despairs and will not come to claim it.

Rambam (11): He need not bring it if Shimon pardoned all but less than a Perutah of the principal.

Rosh (9:21): If Reuven stole a Perutah from Shimon and swore that he did not, Reuven must return it, even if Shimon is in Madai. Since he swore, he cannot bring his (Asham for) atonement until returning it to Shimon himself.

Rosh (24): Even though Korban and Chomesh do not apply nowadays, one who swore must pursue the owner even to Madai to fulfill the Mitzvah of returning theft. If he did not swear, he merely informs him 'I stole this from you. Send to take it.' The Halachah follows Version #2 of Rav Papa (we are not concerned lest the theft become worth a Perutah).

Poskim

Shulchan Aruch (CM 367:1): If Reuven stole from Shimon, even if he denied it, if he did not swear, if he later admits, he need not pursue Shimon to return it. Rather, Reuven holds it until Shimon comes (Rema - and he informs Shimon) to take it.

SMA (2,4): Also this is an enactment to help penitents. If not, it would be proper to make him bring it to where Shimon is.

Rebuttal (Shach 1,2): Letter of the law he need not pursue him to return it, even to be Yotzei Yedei Shamayim,. It is not an enactment!

SMA (3): The Tur connotes that he must send to inform him, just he need not send the theft and accept responsibility for loss on the way. The Rambam connotes that he need not inform him; he holds it until Shimon comes by himself. The Rema teaches that when Shimon comes to Reuven's city, Reuven must inform him that he is ready to give the theft to him.

Shach (3): Also the Bach, Maharshal and Tosfos Yom Tov explain the Rambam like this. I say that the Rambam and Shulchan Aruch agree that he must send to inform him. They merely teach that he need not send the theft. The Rema teaches this, that he must send to inform Shimon wherever Shimon is. Ir Shushan agrees. Rava said 'since... and he admitted to him (i.e. he informed him), it is as if Shimon said 'the theft is like a deposit with you.' If not, all agree that he must return it to be Yotzei Yedei Shamayim. One must make all efforts to inform him. Until he does, he is not Yotzei Yedei Shamayim according to R. Tarfon, and is not Yotzei letter of the law according to R. Akiva.

Rebuttal #1 (Gra 1): The Rambam and Shulchan Aruch say that (only) when Reuven swore, he must pursue him to return it, for Shimon despaired. It must be that their text in the Gemara didn't say 'since he knows whom he stole from and admitted to him.' Rather, even if he did not admit to him, Shimon agrees that it be a deposit.) The Rema and Tur are like our text.

Rebuttal #2 (Ketzos ha'Choshen 1): The Rashba (104a DH Ela) says that since Reuven knows from whom he stole and admits and did not swear, Shimon doesn't benefit if the theft is in Beis Din. It is like a deposit. This applies even if Reuven never admitted, as long as he wants to return it.

Shulchan Aruch (ibid): If Reuven swore about a Perutah or more, he must pursue him to return it, even if Shimon lives overseas, for Shimon despaired after Reuven swore, and will not come to claim it.

Bach (1): If he swore, even if Shimon said 'the theft is like a deposit with you', Reuven must return it, for he needs atonement. If he did not swear, it is a deposit until Shimon comes for it. The Tur holds that this is only if he admitted before Shimon went to Madai. If in front of Shimon he denied, and he admitted in Beis Din after Shimon went to Madai, even though he need not bring it to Madai, he must inform him. Also the Rosh says so. The Rambam did not specify that he must inform him.

Rebuttal (Shach 4): The Tur can explain that this is even if he did not admit before Shimon left. Even though he need not bring it to Madai, he must inform him. Also, even if Reuven swore, if Shimon agreed that the theft be a deposit with him, Reuven need not bring it to him. Tosfos (104a DH Omar) says so explicitly. Rather, he admitted in front of witnesses, not in front of Shimon

SMA (4): If he swore he must return it to him, for it says "la'Asher Hu Lo Yitnenu b'Yom Ashmaso."

Rebuttal (Shach 5): Also Ir Shushan says so. The Gemara rejected this! Rather, since he needs atonement, he must return it to him. Perhaps they explain that the Gemara gives the reason for the verse. There was no need to explain like this.

Defense (Ketzos ha'Choshen 2): The Gemara explains that he needs atonement due to this verse, therefore, he must return it to him!

Shach (6): The Shulchan Aruch cites the Rambam. They connote that if Reuven informs Shimon, he will come to claim it, so Reuven need not bring it to him. The Maharshal and Tosfos Yom Tov say so. I disagree. He wrote that he must pursue him! Rather, the Rambam teaches that even if he informed him he must pursue him, for once he swore Shimon thinks that he will not return it, even though he informs him now. However, why did he find a new reason? The Gemara says that he must return it to get atonement! This is even if we know that Shimon did not despair! The Maharshal says that if Reuven informed him and Shimon said 'hold onto it', he must return it to get atonement. This is if he sent to inform him. If he told Shimon directly, if Shimon left it with him, it is as if he deposited it with him.

Shulchan Aruch (3): If Reuven returned it all, or Shimon pardoned it all, except for less than a Perutah, Reuven need not go to return it. Even if the theft is intact, we are not concerned lest it rise in value to a Perutah.

Beis Yosef (DH u'Mah she'Chosav Afilu): It is known that the Halachah follows the latter version. The Gemara connotes that if it became worth a Perutah, one must return it. The Ramah says so, and the Rambam connotes like this. The Ri exempts even if it becomes worth a Perutah.