כט אֵשֶׁת אִישׁ שֶׁאוֹמֶרֶת עַל הָעֻבָּר שֶׁאֵינוֹ מִבַּעְלָהּ, אֵינָהּ נֶאֱמֶנֶת לְפָסְלוֹ. הַגָּה: וְיֵשׁ אוֹמְרִים דַּוְקָא בִנְּשׂוּאָה, שֶׁיֵּשׁ לַבֵּן חֶזְקַת כַּשְׁרוּת. אֲבָל אֲרוּסָה שֶׁאוֹמֶרֶת עַל בְּנָהּ שֶׁהוּא מַמְזֵר, אַף עַל פִּי שֶׁהָאָרוּס אוֹמֵר שֶׁהוּא שֶׁלּוֹ וְשֶׁלֹּא זָזָה יָדוֹ מִתּוֹךְ יָדָהּ, יֵשׁ אוֹמְרִים דְּהַבֵּן הָוֵי סְפֵק מַמְזֵר, וְיֵשׁ אוֹמְרִים דְּהוּא נֶאֱמָן (סְבָרַת הָרַב דִּבְאָרוּס מַיְרֵי דִּבְרֵי נ"י פֶּרֶק אַלְמָנָה בְּנִדּוֹן זֶה שֶׁהֵבִיא ב' דֵּעוֹת אֵלּוּ). אֲבָל הָאָב שֶׁאוֹמֵר עַל הָעֻבָּר שֶׁאֵינוֹ מִמֶּנּוּ, אוֹ עַל אֶחָד מִבָּנָיו שֶׁאֵינוֹ בְּנוֹ, נֶאֱמָן לְפָסְלוֹ וְהוּא מַמְזֵר וַדַּאי. וְאִם יֵשׁ בָּנִים לַבֵּן, אֵינוֹ נֶאֱמָן אַף עַל הַבֵּן. וְאִם הִיא אוֹמֶרֶת: מֵגּוֹי אוֹ מֵעֶבֶד נִתְעַבַּרְתִּי, הַוָּלָד כָּשֵׁר שֶׁאֵין הַבַּעַל יָכוֹל לְהַכְחִישָׁהּ בַּזֶּה. הַגָּה: וְהָא דְּאָב נֶאֱמָן עַל בְּנוֹ, הַיְנוּ דַּוְקָא שֶׁלֹּא הָיָה לוֹ חֶזְקַת כַּשְׁרוּת עַל פִּי הָאָב, אֲבָל הָוֵי לֵהּ חֶזְקַת כַּשְׁרוּת עַל פִּי הָאָב שׁוּב (הָאָב) אֵינוֹ נֶאֱמָן עָלָיו רַק בְּסָהֲדֵי (ר"י בְּשֵׁם הָרְמַ"ה). הָאָב שֶׁאָמַר עַל בְּנוֹ שֶׁהוּא מַמְזֵר, וְחָזַר אַחַר כָּךְ וְנָתַן אֲמַתְלָא לִדְבָרָיו לָמָּה דִּבֵּר בִּתְחִלָּה כָּךְ, נֶאֱמָן (מהר"מ מֵרִיזְבּוּרְק). הָא דְּאָב נֶאֱמָן עַל בְּנוֹ הַיְנוּ בְּמִי שֶׁהוּא בְּחֶזְקַת אָבִיו, כְּגוֹן בְּאִשְׁתּוֹ נְשׂוּאָה, אֲבָל פְּנוּיָה שֶׁאוֹמֶרֶת: זֶהוּ בֶּן פְּלוֹנִי, וְהוּא אוֹמֵר שֶׁמִּמַּמְזֵר נִתְעַבְּרָה, אֵינוֹ נֶאֱמָן לְפָסְלוֹ וְהִיא נֶאֱמֶנֶת עָלָיו לְהַכְשִׁירוֹ (ת"ה סִימָן רס"ז):
29 A married woman that says about her fetus that he is not from her husband, she is not believed to invalidate him. HG"H - There are those that say, specifically with a woman married through nissuin, that the son has a assumption (chazakah) of being valid. But a women only married through arusin that she says her son is a mamzer, even though the engaged husband says that it is his, and that his hand did not move from her's. There are those that say, that the son is a doubt of a mamzer, and there are those that say he is believed. But a father that says on a fetus that it is not from him, or on one of his sons that it is not his son, he is believed to invalidate him and he is a absolute mamzer. And if there are sons to the son, he is not believed even on the son. And if she says: "from a idol worshiper or from a slave I became pregnant," the baby is valid because the husband is not able to contradict her on this. HG"H- This that the father is believed on the son this is specifically that he didn't have a assumption of validity from the father's mouth, but if he had a assumption of validity, furthermore the father is not believed unless with witnesses (Ri in the name of Ramah), The father that says on his son that he is a mamzer, and retracts and says an excuse for why he said it, he is believed. That which the father is believed about the son, that is where he is in the father's control, for example, with his wife in nisuin, but a unmarried woman who says "this is Plony's son," and he says "she was impregnated from a mamzer," he is not believed to invalidate him, but he is believed to make him valid.