TT #641 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:05
When brothers dwell together and one of them dies and has no son, the wife of the dead shall not be outside to a strange man; her husband’s brother shall come upon her and take her to himself as a wife and perform the duty of a husband’s brother for her.
Torah Temimah points to Yevamot / Sifrei (via TT).
TT lemma: כִּי יֵשְׁבוּ.
אָמַר רַב שֵׁשֶׁת אָמַר רַבִּי אֶלְעָזָר מִשּׁוּם רַבִּי אֶלְעָזָר בֶּן עֲזַרְיָה: מִנַּיִן לְיִבְמָה שֶׁנִּפְלָה לִפְנֵי מוּכֵּה שְׁחִין שֶׁאֵין חוֹסְמִין אוֹתָהּ? שֶׁנֶּאֱמַר לֹא תַחְסֹם שׁוֹר בְּדִישׁוֹ, וּסְמִיךְ לֵיהּ כִּי יֵשְׁבוּ אַחִים יַחְדָּו.
English: Rav Sheshet said in the name of Rabbi Elazar in the name of Rabbi Elazar ben Azariah: From where do we know that a yevamah who falls before a brother afflicted with boils is not silenced (forced to accept yibbum)? As it is said “You shall not muzzle an ox while it is threshing,” and immediately next to it “When brothers dwell together.”
On the daf / in context: The juxtaposition teaches that just as one may not muzzle the ox, one may not force the yevamah to remain with a repulsive brother; he is compelled to perform chalitzah instead.
Derash from juxtaposition (semikhut) with the muzzling prohibition.
A yevamah is not forced to accept yibbum with a brother who is afflicted with boils; he is compelled to give chalitzah.