TT #674 · 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 Kiddushin 14a / Yevamot.
TT lemma: יְבָמָהּ יָבֹא עָלֶיהָ וּלְקָחָהּ לוֹ לְאִשָּׁה.
הַיְּבָמָה נִקְנֵית בְּבִיאָה, דַּאֲמַר קְרָא יְבָמָהּ יָבֹא עָלֶיהָ וּלְקָחָהּ לוֹ לְאִשָּׁה.
English: The yevamah is acquired by intercourse, for Scripture says “her yavam shall come upon her and take her to himself as a wife.”
On the daf / in context: The verse itself is the source for the unique mode of acquisition in yibbum.
Derash identifying the legal mechanism of acquisition.
Intercourse is the primary and sufficient mode of acquiring the yevamah.