Halacha

הלכה א
כָּל מִי שֶׁנִּתְחַיֵּב מָמוֹן לַחֲבֵרוֹ הַיִּשְׂרָאֵל וְכָפַר בּוֹ וְנִשְׁבַּע עַל שֶׁקֶר הֲרֵי זֶה חַיָּב לְהַחְזִיר לוֹ הַקֶּרֶן שֶׁכָּפַר בּוֹ וְהוֹסָפַת חֹמֶשׁ. וְחַיָּב בְּקָרְבָּן וְהוּא הַנִּקְרָא אֲשַׁם גְּזֵלוֹת:
כסף משנה
1.
Whenever a person becomes financially obligated to a fellow Jew, denies that obligation and takes a false oath to support his denial, should he later admit his obligation he is liable to return the principal that he denied plus a surcharge of one fifth of the new total. He is also liable to bring a sacrifice, which is called a guilt offering, for robbery.

הלכה ב
אֶחָד הַגּוֹזֵל אוֹ הָעוֹשֵׁק אוֹ הַגּוֹנֵב אוֹ שֶׁהִלְוָהוּ אוֹ שֶׁהִפְקִיד אֶצְלוֹ אוֹ מָצָא אֲבֵדָה וְכִחֵשׁ בָּהּ אוֹ שֶׁהָיְתָה בֵּינֵיהֶן שֻׁתָּפוּת וְנִשְׁאַר לוֹ אֶצְלוֹ מָמוֹן אוֹ שֶׁעָשָׂה לוֹ מְלָאכָה וְלֹא נָתַן לוֹ שְׂכָרוֹ. כְּלָלוֹ שֶׁל דָּבָר כָּל שֶׁאִלּוּ הוֹדָה חַיָּב לְשַׁלֵּם בְּדִין וְכָפַר וְנִשְׁבַּע מְשַׁלֵּם קֶרֶן וְחֹמֶשׁ שֶׁנֶּאֱמַר (ויקרא ה כא) "וְכִחֵשׁ בַּעֲמִיתוֹ בְּפִקָּדוֹן":
כסף משנה
2.
The above applies to any of the following: one who robbed, one who withheld money due a colleague, one who stole, one who took a loan, one who was given an entrusted article, one who discovered a lost article and denied it, a partner with whom money belonging to the partnership remained, and an employer for whom a worker performed work, but was not paid.
To state the general principle: Whenever a person who admitted the obligation would be obligated by law to pay, he must pay the principal and a fifth if he denies his obligation, as Leviticus 5:21 says: "If he denies his colleague's claim regarding an entrusted object...."

הלכה ג
בַּמֶּה דְּבָרִים אֲמוּרִים בְּשֶׁהָיָה חַיָּב לְשַׁלֵּם מֵחֲמַת עַצְמוֹ. אֲבָל אִם הָיָה חַיָּב לְשַׁלֵּם מֵחֲמַת אָבִיו אֵינוֹ מְשַׁלֵּם חֹמֶשׁ. כֵּיצַד. כְּגוֹן שֶׁגָּזַל אָבִיו אוֹ גָּנַב אוֹ שֶׁהָיָה חַיָּב לַאֲחֵרִים וְהַבֵּן יוֹדֵעַ וְכָפַר הַבֵּן וְנִשְׁבַּע וְאַחַר כָּךְ הוֹדָה מְשַׁלֵּם הַקֶּרֶן בִּלְבַד שֶׁנֶּאֱמַר (ויקרא ה כג) "אֲשֶׁר גָּזָל" עַל גְּזֵלוֹ הוּא מוֹסִיף חֹמֶשׁ וְאֵינוֹ מוֹסִיף חֹמֶשׁ עַל גֵּזֶל אָבִיו:
כסף משנה
3.
When does the above apply? When the person is obligated to pay because of his own actions. When, however, he is liable because of his father, he is not liable for the additional fifth.
What is implied? If one's father robbed or stole or was in debt to others, and the son knew of the matter, and after the father's death the son denied the claim, took an oath and afterwards admitted his liability, he need pay only the principal. For Leviticus 5:23 states: "that he obtained by robbery," implying that one is liable for an additional fifth for one's own robbery, but not for robbery committed by one's father.

הלכה ד
בַּמֶּה דְּבָרִים אֲמוּרִים בְּשֶׁאֵין הַגְּזֵלָה קַיֶּמֶת. אֲבָל אִם גָּזַל אָבִיו וּמֵת וְהַגְּזֵלָה קַיֶּמֶת וְכָפַר הַיּוֹרֵשׁ וְנִשְׁבַּע וְאַחַר כָּךְ הוֹדָה מְשַׁלֵּם קֶרֶן וְחֹמֶשׁ:
כסף משנה
4.
When does the above apply? When the object obtained by robbery no longer exists. Different laws apply however, when a person's father obtained an object by robbery and then died, and the object still exists. If the heir denies his obligation, takes an oath to that effect and then admits his liability, he is liable for the principal and the addition of a fifth.

הלכה ה
גָּזַל הָאָב וְנִשְׁבַּע הָאָב וְהוֹדָה וְאַחַר כָּךְ מֵת הֲרֵי הַיּוֹרֵשׁ מְשַׁלֵּם קֶרֶן וְחֹמֶשׁ:
כסף משנה
5.
If the father committed robbery, took a false oath, admitted his guilt and then died, his heir must pay the principal and the addition of a fifth.

הלכה ו
גָּזַל וְנִשְׁבַּע וּמֵת וְהוֹדָה הַיּוֹרֵשׁ מְשַׁלֵּם הַקֶּרֶן בִּלְבַד. וּבֵין כָּךְ וּבֵין כָּךְ הַיּוֹרֵשׁ פָּטוּר מִן הָאָשָׁם:
כסף משנה
6.
If the father committed robbery, took a false oath and then died, and the heir admitted the father's guilt, the heir is liable to pay only the principal.
In either instance, the heir is not obligated to bring the guilt offering.

הלכה ז
הַנִּשְׁבָּע לְעַכּוּ''ם מְשַׁלֵּם אֶת הַקֶּרֶן וְאֵינוֹ חַיָּב בְּחֹמֶשׁ שֶׁנֶּאֱמַר (ויקרא ה כא) "וְכִחֵשׁ בַּעֲמִיתוֹ". וְכֵן הַגּוֹזֵל פָּחוֹת מִשְּׁוֵה פְּרוּטָה וְכָפַר וְנִשְׁבַּע אֵינוֹ חַיָּב בְּחֹמֶשׁ שֶׁאֵין פָּחוֹת מִשְּׁוֵה פְּרוּטָה מָמוֹן. כַּמָּה הוּא הַחֹמֶשׁ. אֶחָד מֵאַרְבָּעָה בְּקֶרֶן שֶׁאִם גָּזַל שְׁוֵה אַרְבָּעָה וְנִשְׁבַּע מְשַׁלֵּם חֲמִשָּׁה. וְאִם הָיְתָה הַגְּזֵלָה קַיֶּמֶת מַחְזִיר אוֹתָהּ וְנוֹתֵן דְּמֵי רְבִיעַ שֶׁלָּהּ:
כסף משנה
7.
A person who takes a false oath in response to the claim of a gentile and later admits his guilt is obligated to pay the principal, but not the additional fifth, for Leviticus 5:21 speaks of one who "denies his colleague's claim."
Similarly, a person who takes less than the worth of a p'rutah by robbery, denies the charge and takes a false oath to that effect is not liable to pay an additional fifth, for anything less than a p'rutah's worth is not considered a significant financial responsibility.
What is meant by an additional fifth? One fourth of the principal. For example, if a person obtained four zuz by robbery and took a false oath, he must pay five. If the object obtained by robbery itself still exists, it must be returned and a fourth of its value added.

הלכה ח
אֵין הַנִּשְׁבָּע עַל כְּפִירַת מָמוֹן מְשַׁלֵּם חֹמֶשׁ עַד שֶׁיּוֹדֶה מֵעַצְמוֹ. אֲבָל אִם בָּאוּ עֵדִים וְהוּא עוֹמֵד בִּכְפִירָתוֹ מְשַׁלֵּם הַקֶּרֶן בִּלְבַד עַל פִּי עֵדִים וְאֵינוֹ מְשַׁלֵּם אֶת הַחֹמֶשׁ. שֶׁהַחֹמֶשׁ עִם הַקָּרְבָּן לְכַפָּרָה הֵם בָּאִים וְאֵינוֹ מְבִיאָן אֶלָּא עַל פִּי עַצְמוֹ:
כסף משנה
8.
A person who takes a false oath denying a financial claim is not liable to pay an additional fifth unless he himself admits his guilt. If, however, witnesses come and despite his continued denial establish his guilt through their testimony, he is liable to pay only the principal, but not the additional fifth.
The rationale is that the additional fifth and the sacrifice were instituted for the sake of atonement. Therefore, he is obligated for them only when it is his admission that makes him liable.

הלכה ט
הַגּוֹזֵל אֶת חֲבֵרוֹ אַף עַל פִּי שֶׁכָּפַר בּוֹ הוֹאִיל וְלֹא נִשְׁבַּע אִם חָזַר וְהוֹדָה אֵינוֹ חַיָּב לִרְדֹּף אַחַר הַבְּעָלִים עַד שֶׁיַּחְזִיר לָהֶם מָמוֹן שֶׁבְּיָדוֹ אֶלָּא יְהֵא בְּיַד הַגַּזְלָן עַד שֶׁיָּבוֹאוּ הַבְּעָלִים וְיִטְּלוּ שֶׁלָּהֶן. אֲבָל אִם נִשְׁבַּע עַל שְׁוֵה פְּרוּטָה וָמַעְלָה חַיָּב לִרְדֹּף אַחַר הַבְּעָלִים עַד שֶׁיַּחְזִיר לָהֶם אֲפִלּוּ הֵם בְּאִיֵּי הַיָּם. מִפְּנֵי שֶׁכְּבָר נִתְיָאֲשׁוּ מֵאַחַר שֶׁנִּשְׁבַּע וְאֵינָן בָּאִין עוֹד לְתָבְעוֹ:
כסף משנה
9.
When a person robs from a colleague, even if he denied the robbery - as long as he did not take a false oath - if he afterwards admits his guilt he is not liable to seek out the owner to return the money in his possession. Instead, it may remain in the possession of the robber until the owners come and take his due.
If, however, he took a false oath concerning property worth a p'rutah or more, he is obligated to seek out the owner to return the money to him even if he is on far removed islands. The rationale is that once the robber took a false oath, the owner has despaired of the return of his property and will not demand it again.

הלכה י
אֲפִלּוּ הֶחְזִיר הַגְּזֵלָה כֻּלָּהּ חוּץ מִשְּׁוֵה פְּרוּטָה חַיָּב לְהוֹלִיכָהּ אַחַר הַנִּגְזָל. וְלֹא יִתֵּן לֹא לִבְנוֹ שֶׁל נִגְזָל וְלֹא לִשְׁלוּחוֹ אֶלָּא אִם כֵּן עָשָׂה הַנִּגְזָל הַשָּׁלִיחַ בְּעֵדִים. וְאִם הֵבִיא אֶת הַגְּזֵלָה וְאֶת הַחֹמֶשׁ לְבֵית דִּין שֶׁבְּעִירוֹ הֲרֵי זֶה מֵבִיא אָשָׁם וּמִתְכַּפֵּר לוֹ וּבֵית דִּין מְטַפְּלִין בָּהּ עַד שֶׁתַּגִּיעַ לְבַעֲלָהּ. וְכֵן נוֹתֵן הוּא לִשְׁלִיחַ בֵּית דִּין. וְכָל הַנּוֹתֵן הַגְּזֵלָה וְכַיּוֹצֵא בּוֹ לְבֵית דִּין יָצָא:
כסף משנה
10.
Even if a robber returned the entire worth of the object obtained by robbery with the exception of a p'rutah, he is obligated to bring it to the original owner. He may not give the p'rutah to the owner's son or agent unless the owner appointed an agent for this purpose in the presence of witnesses.
If the robber brings the principal and the additional fifth to the Rabbinic court in his city, he may bring a guilt offering and gain atonement thereby. The court will then ensure that the object obtained by robbery will reach its original owner. Similarly, the robber may give the article to an agent of the court. Whenever a person returns an object obtained by robbery or the like to a Rabbinic court, he has fulfilled his obligation to return it.

הלכה יא
נָתַן לוֹ אֶת הַקֶּרֶן וְלֹא נָתַן לוֹ אֶת הַחֹמֶשׁ אוֹ שֶׁמָּחַל לוֹ עַל הַקֶּרֶן וְלֹא מָחַל לוֹ עַל הַחֹמֶשׁ אוֹ שֶׁמָּחַל לוֹ עַל זֶה וְעַל זֶה חוּץ מִפָּחוֹת מִשְּׁוֵה פְּרוּטָה בַּקֶּרֶן אֵינוֹ צָרִיךְ לְהוֹלִיךְ אַחֲרָיו אֶלָּא יָבוֹא הַנִּגְזָל וְיִטּל אֶת הַשְּׁאָר. וְאַף עַל פִּי שֶׁהַגְּזֵלָה עַצְמָהּ קַיֶּמֶת אֵין חוֹשְׁשִׁין שֶׁמָּא תִּתְיַקֵּר וְנִמְצָא הַנִּשְׁאָר שְׁוֵה פְּרוּטָה. אֲבָל אִם נָתַן לוֹ אֶת הַחֹמֶשׁ וְלֹא נָתַן לוֹ אֶת הַקֶּרֶן אוֹ שֶׁמָּחַל לוֹ עַל הַחֹמֶשׁ וְלֹא מָחַל לוֹ עַל הַקֶּרֶן אוֹ שֶׁמָּחַל לוֹ עַל זֶה וְעַל זֶה חוּץ מִשְּׁוֵה פְּרוּטָה בַּקֶּרֶן חַיָּב לְהוֹלִיכוֹ אַחֲרָיו אוֹ לָתֵת לְבֵית דִּין שֶׁבְּעִירוֹ כְּמוֹ שֶׁבֵּאַרְנוּ:
כסף משנה
11.
When the robber gave the original owner the principal, but not the additional fifth, the owner waived payment of the principal but not of the additional fifth, or he waived payment of both with the exception of less than a p'rutah's worth of the principal, the robber does not have to seek out the owner. Instead, when the owner comes he will take the remainder of what is due him.
This ruling is followed when the owner waives payment of everything but less than a p'rutah's worth of the principal even when the object obtained by robbery itself exists. We do not suspect that perhaps the value of the article will increase, and thus the portion remaining will become worth a p'rutah.
If, however, the robber gave the owner the additional fifth, but did not give him the principal, or if the owner waived payment of the additional fifth but not of the principal, or he waived payment of both with the exception of a p'rutah's worth of the principal, the robber must seek out the owner or give the money to the Rabbinic court in his town, as explained in the previous halachot.

הלכה יב
הַמַּחֲזִיר אֶת הַקֶּרֶן לַבְּעָלִים וְכָפַר פַּעַם שְׁנִיָּה בַּחֹמֶשׁ וְנִשְׁבַּע עָלָיו נַעֲשָׂה הַחֹמֶשׁ כְּקֶרֶן לְכָל דָּבָר וּמְשַׁלֵּם עָלָיו חֹמֶשׁ אַחֵר שֶׁנֶּאֱמַר (ויקרא ה כד) "וַחֲמִשִׁתָיו יֹסֵף עָלָיו" מְלַמֵּד שֶׁהוּא מוֹסִיף חֹמֶשׁ עַל חֹמֶשׁ עַד שֶׁיִּתְמַעֵט הַחֹמֶשׁ שֶׁיִּכְפֹּר בּוֹ וְנִשְׁבַּע עָלָיו מִשְּׁוֵה פְּרוּטָה:
כסף משנה
12.
If the robber returned the principal to the owner after denying his claim and taking a false oath and then denied owing him the additional fifth and took a false oath concerning this, the additional fifth is considered as part of the principal with regard to all matters, and the robber must pay another fifth because of it.
This is derived from Leviticus 5:24, which states: "And he shall add its fifths." The use of the plural teaches that he must add a fifth to a fifth if he continues to take false oaths until the fifth that he denies - and concerning which he takes a false oath - is worth less than a p'rutah.

הלכה יג
מִי שֶׁהָיָה אֶצְלוֹ פִּקָּדוֹן וְטָעַן שֶׁאָבַד וְנִשְׁבַּע וְחָזַר וְהוֹדָה שֶׁהוּא אֶצְלוֹ. וְחָזַר וְטָעַן שֶׁאָבַד וְנִשְׁבַּע וְחָזַר וְהוֹדָה שֶׁהוּא אֶצְלוֹ מְשַׁלֵּם חֹמֶשׁ לְכָל שְׁבוּעָה וּשְׁבוּעָה עִם הַקֶּרֶן הָאֶחָד שֶׁנֶּאֱמַר (ויקרא ה כד) "וַחֲמִשִׁתָיו יֹסֵף עָלָיו" מְלַמֵּד שֶׁהוּא מְשַׁלֵּם כַּמָּה חֳמָשִׁין עַל קֶרֶן אֶחָד:
כסף משנה
13.
The following rule applies with regard to a person who had been entrusted with an object for safekeeping and who repeatedly took false oaths concerning the entrusted article. For example, the watchman claimed that the article was lost, took a false oath to support his claim and then admitted that it was in his possession. He then claimed it was lost and took a second false oath and then admitted it was in his possession. He must pay an additional fifth for every false oath, plus the principal.
This is derived from the phrase cited above: "And he shall add its fifths." The use of the plural teaches that he must pay several fifths for one principal.

נזיקין הלכות גזילה ואבידה פרק ז
Nezikim Gezeilah and Aveidah Chapter 7