TT #651 · 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 22b.
TT lemma: וּבֵן אֵין לוֹ.
אֵין לוֹ – עַיֵּן עָלָיו, אִם יֵשׁ לוֹ בֵּן מִכָּל מָקוֹם.
English: “He has no son” — examine him: if he has a son from anywhere (any wife), there is no yibbum.
On the daf / in context: The absence of a son is absolute; a son from another wife also exempts the present widow.
Derash on the absolute absence of offspring.
A son from any wife of the deceased releases all of his widows from yibbum.