TT #662 · 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 39a.
TT lemma: יְבָמָהּ יָבֹא עָלֶיהָ.
מִצְוַת יִבּוּם קוֹדֶמֶת לְמִצְוַת חֲלִיצָה, דִּכְתִיב יְבָמָהּ יָבֹא עָלֶיהָ – מִצְוָה.
English: The mitzvah of yibbum takes precedence over the mitzvah of chalitzah, for it is written “her yavam shall come upon her” — this is the mitzvah.
On the daf / in context: The positive command to perform yibbum is primary; chalitzah is the alternative when yibbum is not performed.
Derash establishing priority of yibbum over chalitzah.
Yibbum is the preferred fulfillment; chalitzah is secondary.