175 Yevamot 15/8-9

(ח) הָאִשָּׁה שֶׁהָלְכָה הִיא וּבַעְלָהּ לִמְדִינַת הַיָּם וּבְנָהּ עִמָּהֶם, וּבָאָה וְאָמְרָה מֵת בַּעְלִי וְאַחַר כָּךְ מֵת בְּנִי, נֶאֱמֶנֶת. מֵת בְּנִי וְאַחַר כָּךְ מֵת בַּעְלִי, אֵינָהּ נֶאֱמֶנֶת, וְחוֹשְׁשִׁים לִדְבָרֶיהָ, וְחוֹלֶצֶת וְלֹא מִתְיַבֶּמֶת:

(ט) נִתַּן לִי בֵן בִּמְדִינַת הַיָּם, וְאָמְרָה מֵת בְּנִי וְאַחַר כָּךְ מֵת בַּעְלִי, נֶאֱמֶנֶת. מֵת בַּעְלִי וְאַחַר כָּךְ מֵת בְּנִי, אֵינָהּ נֶאֱמֶנֶת, וְחוֹשְׁשִׁים לִדְבָרֶיהָ, וְחוֹלֶצֶת וְלֹא מִתְיַבֶּמֶת:

(8) [If] a woman and her husband went overseas and her son was with them, and she came and said, "My husband died and then my son died", she is trusted. [If she said], "My son died and then my husband died", she is not trusted. But we are worried about her claim and she performs Chalitzah [the ceremony releasing the widow of a childless man from the obligation of Levirate marriage] but does not undergo Yibum [Levirate marriage wherein a man weds his childless brother's widow].

(9) [If] a woman [states], "I was given a son [that is, she bore a son] overseas", and then states "My son died and then later my husband died", she is trusted; [but if she states], "My husband died and then later my son died", she is not trusted. But we are worried about her claim and she performs Chalitzah but does not undergo Yibum.