Reference for Ketubot 5:3
הַיָּבָם אֵינוֹ מַאֲכִיל בַּתְּרוּמָה. עָשְׂתָה שִׁשָּׁה חֳדָשִׁים בִּפְנֵי הַבַּעַל וְשִׁשָּׁה חֳדָשִׁים בִּפְנֵי הַיָּבָם, וַאֲפִלּוּ כֻלָּן בִּפְנֵי הַבַּעַל חָסֵר יוֹם אֶחָד בִּפְנֵי הַיָּבָם, אוֹ כֻלָּן בִּפְנֵי הַיָּבָם חָסֵר יוֹם אֶחָד בִּפְנֵי הַבַּעַל, אֵינָהּ אוֹכֶלֶת בַּתְּרוּמָה. זוֹ מִשְׁנָה רִאשׁוֹנָה. בֵּית דִּין שֶׁל אַחֲרֵיהֶן אָמְרוּ, אֵין הָאִשָּׁה אוֹכֶלֶת בַּתְּרוּמָה, עַד שֶׁתִּכָּנֵס לַחֻפָּה:
A yavam does not cause (a yevamah) to eat terumah [when she is still awaiting yibum, it being written (Leviticus 22:11): "And a Cohein, if he acquire a soul, the acquisition of his money," and she is the "acquisition of his brother.] If she spent six months before her husband, [six of these twelve months set aside for her after having been solicited by the husband] and six months before the yavam, or even all of them before the husband and six of them before the yavam, or even all of them before the husband and one of them before the yavam [Even though most of them were before the husband, there is a double reservation here: a) he was not obligated to feed her in his lifetime; b) even if he was obligated to feed her in his lifetime, she did not eat after his death, the "acquisition of his money," having been dissolved (but if all of them were before the husband, she could at least have eaten in his lifetime)], or all before the yavam less one day before the husband [and, it goes without saying, if all of them were before the yavam], she does not eat terumah. This is (in accordance with) the first Mishnah [that if the time arrives, she eats terumah]. The beth-din after them ruled: A woman does not eat terumah until she enters the chuppah. [For we fear lest he find a blemish in her, so that she be found to be a "stranger" (to the priesthood) retroactively and his "purchase" be a mistaken one. And according to the first Mishnah we do not entertain this apprehension. Neither do we fear that she might give her brothers and sisters to drink (a cup of terumah), for he (her husband) sets aside a place for her, for which reason they permitted her to eat terumah when the time arrived.]