Reference for Yevamot 2:1
כֵּיצַד אֵשֶׁת אָחִיו שֶׁלֹּא הָיָה בְעוֹלָמוֹ. שְׁנֵי אַחִים, וּמֵת אֶחָד מֵהֶם, וְנוֹלַד לָהֶן אָח, וְאַחַר כָּךְ יִבֵּם הַשֵּׁנִי אֶת אֵשֶׁת אָחִיו, וָמֵת, הָרִאשׁוֹנָה יוֹצֵאת מִשּׁוּם אֵשֶׁת אָחִיו שֶׁלֹּא הָיָה בְעוֹלָמוֹ, וְהַשְּׁנִיָּה מִשּׁוּם צָרָתָהּ. עָשָׂה בָהּ מַאֲמָר וָמֵת, הַשְּׁנִיָּה חוֹלֶצֶת וְלֹא מִתְיַבֶּמֶת:
How does "the wife of his brother who was not in his world" [exempt her tzarah]? If there were two brothers and one of them died, and a brother was born to them, [to whom she was yibum-linked, but to whom (the third brother) she is forbidden by reason of "the wife of his brother who was not in his world"], and afterwards the second brother [who had a wife of his own] took his brother's wife in yibum, and he died [without children] — then the first woman [the wife of the first who had already fallen before him once (for yibum)] goes out (i.e., she is not taken in yibum) by reason of "the wife of his brother who was not in his world"; and the second (goes out) by virtue of being her tzarah. If he (the second) made a ma'amar in her (the first brother's wife) and he died [i.e., if he betrothed her with money. With a yevamah, money-betrothal is not bona fide betrothal, but obtains only by ordinance of the scribes. For a yevamah is not acquired by the yavam to be considered a married woman until he lives with her; and in this instance he had not lived with her before he died.], the second wife receives chalitzah [ and she is not exempt by reason of tzarath ervah, because she is not actually her tzarah], and she is not taken in yibum [because ma'amar acquires to a certain extent, and she is tzarath ervah to a certain extent. And wherever bona fide betrothal does not obtain, she receives chalitzah and is not taken yibum.]