Yevamos15: 4
הַכֹּל נֶאֱמָנִים לְהָעִידָהּ, חוּץ מֵחֲמוֹתָהּ, וּבַת חֲמוֹתָהּ, וְצָרָתָהּ, וִיבִמְתָּהּ, וּבַת בַּעְלָהּ. מַה בֵּין גֵּט לְמִיתָה? שֶׁהַכְּתָב מוֹכִיחַ. עֵד אוֹמֵר ,,מֵת”, וְנִשֵּׂאת, וּבָא אַחֵר וְאָמַר ,,לֹא מֵת” — הֲרֵי זוֹ לֹא תֵצֵא.  עֵד אוֹמֵר ,,מֵת”, וּשְׁנַיִם אוֹמְרִים ,,לֹא מֵת”, אַף עַל פִּי שֶׁנִּשֵּׂאת — תֵּצֵא. שְׁנַיִם אוֹמְרִים ,,מֵת”, וְעֵד אוֹמֵר ,,לֹא מֵת” — אַף עַל פִּי שֶׁלֹּא נִשֵּׂאת, תִּנָּשֵׂא.
Everyone is believed to testify for her, except for her mother-in-law, her mother-in-law's daughter, her co-wife, her sister-in-law, and her husband's daughter. Why is there a difference between [testi- mony concerning] a bill of divorce and [testimony concerning] death? Because the document is proof.  [If] one witness said, “He died,” and she remarried, and then another came and said, “He did not die” —- she need not be discharged. [If] one witness said, “He died,” and two [witnesses] said, “He did not die” —- even if she remarried she must be discharged. [If] two [witnesses] said, “He died,” and one witness said, “He did not die” —- even if she had not remarried, she may do so.
Yevamos15: 5
אַחַת אוֹמֶרֶת ,,מֵת” וְאַחַת אוֹמֶרֶת ,,לֹא מֵת”, זוֹ שֶׁאוֹמֶרֶת מֵת תִּנָּשֵׂא וְתִטֹּל כְּתֻבָּתָהּ, וְזוֹ שֶׁאוֹמֶרֶת לֹא מֵת — לֹא תִנָּשֵׂא וְלֹא תִטֹּל כְּתֻבָּתָהּ.  אַחַת אוֹמֶרֶת ,,מֵת” וְאַחַת אוֹמֶרֶת ,,נֶהֱרַג” — רַבִּי מֵאִיר אוֹמֵר: הוֹאִיל וּמַכְחִישׁוֹת זוֹ אֶת זוֹ — הֲרֵי אֵלּוּ לֹא יִנָּשְׂאוּ. רַבִּי יְהוּדָה וְרַבִּי שִׁמְעוֹן אוֹמְרִים: הוֹאִיל וְזוֹ וָזוֹ מוֹדוֹת שֶׁאֵינוֹ קַיָּם — יִנָּשְׂאוּ.  עֵד אוֹמֵר ,,מֵת” וְעֵד אוֹמֵר ,,לֹא מֵת”, אִשָּׁה אוֹמֶרֶת ,,מֵת” וְאִשָּׁה אוֹמֶרֶת ,,לֹא מֵת” — הֲרֵי זוֹ לֹא תִנָּשֵׂא.
[If] one [wife] said he died, and one said he did not die, the one who said he died may marry and collect her kesubah, while the one who said he did not die may not marry or collect her kesubah.  [If] one said, “He died,” and one said, “He was killed” —- R' Meir says: Since they contradict each other they may not remarry; R' Yehudah and R' Shimon say: Since both agree that he is deceased, they may remarry.  [If] one witness said, “He died,” and one witness said, “He did not die,” [or] a woman said, “He died,” and a woman said, “He did not die” —- she may not remarry.