Mishnayos Kesuvos Perek 1 Mishnah 8

If people saw a woman speaking to one man, but they did not recognize him, and they said to her: What is the nature [tivo] of this man? And she said to them: He is a man called so-and-so and he is a priest; Rabban Gamliel and Rabbi Eliezer say: She is deemed credible, and Rabbi Yehoshua says: It is not based on the statement emerging from her mouth that we conduct our lives. Rather, she assumes the presumptive status of one who engaged in intercourse with a Gibeonite or with a mamzer, men of flawed lineage who disqualify her from marrying a priest, until she brings proof supporting her statement.

רָאוּהָ מְדַבֶּרֶת עִם אֶחָד בַּשּׁוּק, אָמְרוּ לָהּ מַה טִּיבוֹ שֶׁל זֶה. אִישׁ פְּלוֹנִי וְכֹהֵן הוּא. רַבָּן גַּמְלִיאֵל וְרַבִּי אֱלִיעֶזֶר אוֹמְרִים, נֶאֱמֶנֶת. וְרַבִּי יְהוֹשֻׁעַ אוֹמֵר, לֹא מִפִּיהָ אָנוּ חַיִּין, אֶלָּא הֲרֵי זוֹ בְחֶזְקַת בְּעוּלָה לְנָתִין וּלְמַמְזֵר, עַד שֶׁתָּבִיא רְאָיָה לִדְבָרֶיהָ: