Halacha

הלכה א
כָּל חָשׁוּד עַל הַשְּׁבוּעָה אֵין מַשְׁבִּיעִין אוֹתוֹ לֹא שְׁבוּעַת הַתּוֹרָה וְלֹא שְׁבוּעָה מִדִּבְרֵיהֶם וְלֹא שְׁבוּעַת הֶסֵּת. וַאֲפִלּוּ רָצָה הַתּוֹבֵעַ אֵין שׁוֹמְעִין לוֹ:
כסף משנה
1.
Whenever it is suspected that a person might take a false oath, no oath - neither a Scriptural oath, a Rabbinic oath, nor a sh'vuat heset - is administered to him. Even if the plaintiff desires that he take this oath, we do not heed his request.

הלכה ב
אֶחָד הַנִּשְׁבָּע לַשֶּׁקֶר שְׁבוּעַת בִּטּוּי. אוֹ שְׁבוּעַת עֵדוּת. אוֹ שְׁבוּעַת הַפִּקָּדוֹן. אוֹ שְׁבוּעַת שָׁוְא. הֲרֵי הוּא חָשׁוּד עַל הַשְּׁבוּעָה. וְכֵן כָּל הַפָּסוּל לְעֵדוּת מִשּׁוּם עֲבֵרָה. בֵּין פַּסְלָנוּת שֶׁל תּוֹרָה כְּגוֹן בַּעֲלֵי רִבִּית וְאוֹכְלֵי נְבֵלוֹת וְגַזְלָנִין. בֵּין פַּסְלָנוּת שֶׁל דִּבְרֵיהֶם כְּגוֹן מִשְׂחָק בְּקֻבִּיָּא וּמַפְרִיחֵי יוֹנִים. הֲרֵי הוּא חָשׁוּד עַל הַשְּׁבוּעָה וְאֵין מַשְׁבִּיעִין אוֹתוֹ:
כסף משנה
2.
A person who took a false oath - whether a sh'vuat bitui, a sh'vuat edut, or a sh'vuat hapikadon - or an unnecessary oath, he is considered suspect to take a false oath.
Similarly, a person who is not acceptable to serve as a witness because he committed a transgression, whether disqualified because of a Scriptural prohibition, e.g., a person who lends at interest, one who eats meat from an animal that was not ritually slaughtered, or a thief, or because of a Rabbinic prohibition, e.g., a dice-player or a dove racer, is considered suspect to take a false oath and we do not administer an oath to him.

הלכה ג
אֵין אָדָם נַעֲשֶׂה חָשׁוּד עַד שֶׁיָּבוֹאוּ עָלָיו עֵדִים שֶׁהוּא עָבַר עֲבֵרָה שֶׁנִּפְסַל בָּהּ. אֲבָל הַמּוֹדֶה מִפִּי עַצְמוֹ שֶׁהוּא חָשׁוּד וְשֶׁעָבַר עֲבֵרָה שֶׁנִּפְסַל בָּהּ. אַף עַל פִּי שֶׁחוֹשְׁשִׁין לוֹ וְאֵין רָאוּי לַעֲשׂוֹתוֹ עֵד בַּתְּחִלָּה. אִם נִתְחַיֵּב שְׁבוּעָה מַשְׁבִּיעִין אוֹתוֹ שֶׁהֲרֵי אוֹמְרִים לוֹ אִם אֱמֶת אַתָּה אוֹמֵר הִשָּׁבַע וְלֹא מִפְּנֵי שֶׁעָבַרְתָּ עֲבֵרָה אָסוּר לְךָ לְהִשָּׁבַע בֶּאֱמֶת. וְאִם שֶׁקֶר אַתָּה אוֹמֵר הוֹדֵה לְבַעַל דִּינְךָ. אֲבָל הַנֶּחְשָׁד בְּעֵדִים אֵין אָנוּ מַאֲמִינִים אוֹתוֹ שֶׁיִּשָּׁבַע:
כסף משנה
3.
A person is not deemed suspect to take a false oath until witnesses testify that he violated the transgression for which he is disqualified. Different rules apply, however, if a person himself admits that he is suspect to take a false oath, because he committed a transgression that disqualifies him.
We consider him under suspicion and it is not appropriate to make him a witness at the outset. Nevertheless, if he is obligated to take an oath, we administer that oath. For we tell him: "If you are telling the truth, take the oath. The fact that you committed a sin does not make it forbidden for you to take a truthful oath. And if you are lying, acknowledge the other litigant's claim." When a person is deemed suspect because of the testimony of witnesses, we do not believe that he will take a truthful oath.

הלכה ד
תַּקָּנַת חֲכָמִים הִיא שֶׁכָּל הַמְחֻיָּב שְׁבוּעָה מִן הַתּוֹרָה עַל טַעֲנַת וַדַּאי. אִם הָיָה חָשׁוּד הֲרֵי הַתּוֹבֵעַ נִשְׁבָּע מִדִּבְרֵיהֶם וְנוֹטֵל מַה שֶּׁטָּעַן. הָיוּ שְׁנֵיהֶם חֲשׁוּדִין חָזְרָה שְׁבוּעָה לַמְחֻיָּב לָהּ שֶׁהוּא הַנִּתְבָּע וּמִתּוֹךְ שֶׁאֵינוֹ יָכוֹל לִשָּׁבַע מְשַׁלֵּם. הָיָה הֶחָשׁוּד שׁוֹמֵר וְטָעַן שֶׁאָבַד הַפִּקָּדוֹן אוֹ נִגְנַב שֶׁכְּנֶגְדוֹ אֵינוֹ יָכוֹל לְהִשָּׁבַע וְלִטּל שֶׁהֲרֵי אֵינוֹ טוֹעֲנוֹ וַדַּאי שֶׁאֲכָלוֹ. לְפִיכָךְ אִם טָעַן בַּעַל הַפִּקָּדוֹן וְאָמַר בְּפָנַי שָׁלַח יָד בְּפִקְדוֹנִי אוֹ פָּשַׁע בּוֹ הֲרֵי הַתּוֹבֵעַ נִשְׁבָּע בְּתַקָּנַת חֲכָמִים וְנוֹטֵל:
כסף משנה
4.
Our Sages ordained that whenever a person who is suspect to take a false oath is obligated to take a Scriptural Oath because of a definite claim, the plaintiff is given the option of taking a Rabbinic oath and may then collect what he claims.
If they were both suspect, the responsibility for taking the oath returns to the one obligated to take it, i.e., the defendant. Since he cannot take the oath, he is required to pay.
If the person who was suspect was a watchman who claims that the entrusted article was lost or stolen, the plaintiff cannot take an oath, because he does not have a definite claim that the watchman consumed it. Therefore, if the owner of the entrusted object claims: "He used my entrusted article for his own purposesin my presence," or "I know that he was negligent," the plaintiff may take an oath as ordained by our Sages and collect the money he claims.

הלכה ה
נִתְחַיֵּב הֶחָשׁוּד שְׁבוּעָה מִדִּבְרֵיהֶם אִם הָיָה מִן הַנִּשְׁבָּעִין וְנוֹטְלִין אֵינוֹ יָכוֹל לְהִשָּׁבַע וְלִטּל אֶלָּא הַנִּתְבָּע שֶׁכְּנֶגְדוֹ יִשָּׁבַע הֶסֵּת וְיִפָּטֵר. וְכֵן פּוֹגֵם שְׁטָרוֹ וְכָל כַּיּוֹצֵא בָּזֶה שֶׁהָיָה חָשׁוּד וְטָעַן הַלּוֶֹה שֶׁפְּרָעוֹ וְאָמַר יִשָּׁבַע לִי הֲרֵי הַנִּתְבָּע נִשְׁבָּע הֶסֵּת וְיִפָּטֵר מִן הַשְּׁטָר:
כסף משנה
5.
The following laws apply if the person suspect to take a false oath was liable to take a Rabbinic oath. If he is one of those who takes an oath and collects, he may not take the oath and collect. Instead, the defendant is allowed to take a sh'vuat heset and then is freed of liability.
Similarly, when a person who is suspect impairs the legal power of his promissory note or the like and the borrower claims to have paid and requires the plaintiff to take an oath, the defendant is given the option of taking the oath, and in that way becoming released from the obligation of the promissory note.

הלכה ו
הָיָה הֶחָשׁוּד מִן הַנִּשְׁבָּעִין בְּטַעֲנַת סָפֵק אֵינוֹ נִשְׁבָּע וְאֵין שֶׁכְּנֶגְדוֹ נִשְׁבָּע לְפִי שֶׁלֹּא נִתְחַיֵּב זֶה שְׁבוּעָה מִן הַתּוֹרָה. וּלְפִי שֶׁאֵין הַתּוֹבֵעַ טוֹעֲנוֹ טַעֲנַת וַדַּאי כְּדֵי שֶׁיִּשָּׁבַע עַל טַעֲנָתוֹ:
כסף משנה
6.
If the person who is suspect was one of those who is required to take an oath because of an indefinite claim, he is not allowed to take the oath, nor does the plaintiff take the oath. The rationale is that the defendant was not obligated to take an oath by Scriptural Law and the plaintiff is not lodging a definite claim against him that he could support with an oath.

הלכה ז
נִתְחַיֵּב הֶחָשׁוּד שְׁבוּעַת הֶסֵּת אֵין שֶׁכְּנֶגְדוֹ נִשְׁבָּע וְנוֹטֵל. שֶׁשְּׁבוּעַת הֶסֵּת עַצְמָהּ תַּקָּנָה הִיא וְלֹא עָשׂוּ לָהּ תַּקָּנָה אַחֶרֶת שֶׁיִּשָּׁבַע הַתּוֹבֵעַ אֶלָּא הֲרֵי הַנִּתְבָּע נִפְטָר בְּלֹא שְׁבוּעָה:
כסף משנה
7.
When a person who is suspect becomes obligated to take a sh'vuat heset, the plaintiff is not given the option of taking the oath and collecting what he claims. The rationale is that a sh'vuat heset is itself a measure ordained for the benefit of the plaintiff. Therefore we did not ordain a second measure for his benefit. Instead, the defendant is released from liability without taking an oath.

הלכה ח
מִי שֶׁנִּתְחַיֵּב שְׁבוּעַת הֶסֵּת וְהָיָה הַתּוֹבֵעַ חָשׁוּד. אֵין הַנִּתְבָּע יָכוֹל לַהֲפֹךְ עָלָיו הַשְּׁבוּעָה שֶׁהֲרֵי אֵין יָכוֹל לְהִשָּׁבַע. אֶלָּא יְשַׁלֵּם אוֹ יִשָּׁבַע הֶסֵּת. וְאֵין שׁוֹמְעִין לָזֶה לִתְלוֹת בְּדָבָר שֶׁאִי אֶפְשָׁר. וַהֲרֵי זֶה כְּמִי שֶׁהָפַךְ שְׁבוּעָתוֹ עַל הַקָּטָן שֶׁאֵין שׁוֹמְעִין לוֹ אֶלָּא אוֹ יִשָּׁבַע הֶסֵּת אוֹ יְשַׁלֵּם:
כסף משנה
8.
When a person is obligated to take a sh'vuat heset and the plaintiff is suspect to take a false oath, the defendant does not have the option of reversing the responsibility to take the oath. For the plaintiff is unable to take the oath. Instead, the defendant must pay the claim or take a sh'vuat heset.
We do not accept his request to make the judgment dependant on an impossible factor. This is comparable to a person who seeks to reverse the responsibility of an oath and place it upon a minor. We do not heed him. Instead, he must either take a sh'vuat heset or pay.

הלכה ט
מִי שֶׁנִּתְחַיֵּב שְׁבוּעָה בֵּין שֶׁל תּוֹרָה בֵּין שֶׁל דִּבְרֵיהֶם וְנִשְׁבַּע וְנָטַל אוֹ נִשְׁבַּע וְנִפְטַר. וְאַחַר כָּךְ בָּאוּ עָלָיו עֵדִים שֶׁהוּא חָשׁוּד. אֵין שְׁבוּעָתוֹ שֶׁנִּשְׁבַּע כְּלוּם וְיֵשׁ לְבַעַל דִּינוֹ לְהוֹצִיא מִיָּדוֹ מַה שֶּׁנָּטַל אוֹ יִשָּׁבַע זֶה שֶׁכְּנֶגְדוֹ וְיִטּל מִמֶּנּוּ:
כסף משנה
9.
The following principle applies when a person was obligated to take an oath - whether of Scriptural or Rabbinic origin - and he took the oath and either collected his claim or was released and afterwards, witnesses came and testified that he was suspect to take a false oath. The oath which he took is of no consequence. The other litigant may expropriate the money which the person who was suspect collected from him or the other litigant may take an oath and collect his claim.

הלכה י
לְעוֹלָם כָּזֶה דָּנִין לֶחָשׁוּד עַד שֶׁיִּלְקֶה בְּבֵית דִּין. אִם הָיוּ עָלָיו עֵדִים שֶׁלָּקָה וְעָשָׂה תְּשׁוּבָה יַחְזֹר לְכַשְׁרוּתוֹ בֵּין לְעֵדוּת בֵּין לִשְׁבוּעָה:
כסף משנה
10.
These principles are applied with regard to a person suspect of taking a false oath until he receives lashes in court. If there are witnesses that he received lashes and repented, his status is restored and he is acceptable both as a witness and to take an oath.

הלכה יא
מִי שֶׁטָּעַן עַל חֲבֵרוֹ וְכָפַר בּוֹ וְנִשְׁבַּע בֵּין שְׁבוּעַת הַתּוֹרָה בֵּין שְׁבוּעַת הֶסֵּת. וְאַחַר כָּךְ בָּאוּ עֵדִים וְהֵעִידוּ עָלָיו שֶׁעַל שֶׁקֶר נִשְׁבַּע. הֲרֵי זֶה מְשַׁלֵּם וְהֻחְזַק חָשׁוּד עַל הַשְּׁבוּעָה. וּכְבָר בֵּאַרְנוּ בִּשְׁבוּעוֹת שֶׁכָּל הַנִּשְׁבָּע עַל מָמוֹן חֲבֵרוֹ וְעָשָׂה תְּשׁוּבָה חַיָּב לְהוֹסִיף חֹמֶשׁ:
כסף משנה
11.
The following rules apply when a person lodges a claim against a colleague, the defendant denies the claim and supports his denial by taking either a Scriptural oath or a Rabbinic oath. If afterwards, witnesses come and testify that he took a false oath, he must pay the claim and is deemed suspect of taking a false oath.
We already explained in Hilchot Sh'vuot, that anyone who takes a false oath with regard to money belonging to his colleague and repents must add an additional fifth.

הלכה יב
טְעָנוֹ שֶׁיֵּשׁ לוֹ חוֹב אֶצְלוֹ בְּעֵדִים וְקִנְיָן וְאָמַר כֵּן הָיָה וּפְרַעְתִּיךָ. אוֹ שֶׁאָמַר אֵינִי חַיָּב לְךָ כְּלוּם וְנִשְׁבַּע. וְאַחַר כָּךְ בָּאוּ עֵדֵי הַקִּנְיָן אוֹ הוֹצִיא הַשְּׁטָר וְנִתְקַיֵּם הֲרֵי זֶה מְשַׁלֵּם וְאֵינוֹ חָשׁוּד. שֶׁהֲרֵי לֹא הֱעִידוֹ שֶׁלֹּא פְּרָעוֹ וְלֹא אָמַר הַנִּתְבָּע לֹא הָיוּ דְּבָרִים מֵעוֹלָם. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
12.
The following rule applies when a plaintiff claims that a defendant owes him a debt which was undertaken in the presence of witnesses and affirmed by a kinyan, and the defendant agrees that originally this was so, but claims to have paid the debt, or the defendant says: "I do not owe you anything," and takes an oath to support either of these claims. If, afterwards, witnesses to the kinyan testify or the plaintiff produces a promissory note and verifies its authenticity, the defendant is obligated to pay. He is not, however, considered as suspect to take a false oath. For the witnesses did not testify that he did not pay. And the defendant did not say: "This never happened." Similar principles apply in all analogous situations.

משפטים הלכות טוען ונטען פרק ב
Mishpatim To`en and Nitan Chapter 2