Midrash for Ketubot 1:5
הָאוֹכֵל אֵצֶל חָמִיו בִּיהוּדָה שֶׁלֹּא בְעֵדִים, אֵינוֹ יָכוֹל לִטְעֹן טַעֲנַת בְּתוּלִים, מִפְּנֵי שֶׁמִּתְיַחֵד עִמָּהּ. אַחַת אַלְמְנַת יִשְׂרָאֵל וְאַחַת אַלְמְנַת כֹּהֵן, כְּתֻבָּתָן מָנֶה. בֵּית דִּין שֶׁל כֹּהֲנִים הָיוּ גוֹבִין לַבְּתוּלָה אַרְבַּע מֵאוֹת זוּז, וְלֹא מִחוּ בְיָדָם חֲכָמִים:
If one had eaten at his in-laws without witnesses in Judah, she is not subject to a claim of virginity, for he is left alone with her. [When they made the betrothal feast in the house of the bride's father in Judah, it was the practice that the groom be left alone with her to become familiar with her. Therefore, when he afterwards married her, he did not have a claim of virginity.] Both the kethubah of the widow of an Israelite and that of the widow of a Cohein are one manah. A beth-din of Cohanim would claim four hundred zuz for (the kethubah of) a virgin (who was the daughter of a Cohein), and the sages did not protest.