Reference for Yevamot 15:2
בֵּית הִלֵּל אוֹמְרִים, לֹא שָׁמַעְנוּ אֶלָּא בְּבָאָה מִן הַקָּצִיר, וּבְאוֹתָהּ מְדִינָה, וּכְמַעֲשֶׂה שֶׁהָיָה. אָמְרוּ לָהֶן בֵּית שַׁמַּאי, אַחַת הַבָּאָה מִן הַקָּצִיר, וְאַחַת הַבָּאָה מִן הַזֵּיתִים, וְאַחַת הַבָּאָה מִן הַבָּצִיר, וְאַחַת הַבָּאָה מִמְּדִינָה לִמְדִינָה. לֹא דִבְּרוּ חֲכָמִים בַּקָּצִיר אֶלָּא בַהֹוֶה. חָזְרוּ בֵית הִלֵּל לְהוֹרוֹת כְּבֵית שַׁמָּאי:
Beth Hillel say: We did not hear (that a woman is permitted to remarry) except when she came from the wheat harvest, and in the same province, and as in the (same) event that transpired, [where men went to harvest wheat, and a snake bit and killed one of them, and his wife came and apprised beth-din of it, and they sent and found her account to be correct. And the sages permitted (a woman to remarry) only in like circumstances — that it have occurred close at hand; but she was not believed (to testify) about what had transpired abroad.] Beth Shammai said to them: (She may remarry) whether she came from the wheat harvest, or the olive harvest, or the grape harvest, and from one province to another. The sages stated "wheat harvest" only in that such happened to be the case, [but the same applies to all places] — whereupon Beth Hillel retracted (their ruling) to rule according to Beth Shammai.