TT #652 · 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.
TT lemma: לֹא תִהְיֶה אֵשֶׁת הַמֵּת הַחוּצָה.
לֹא תִהְיֶה אֵשֶׁת הַמֵּת הַחוּצָה לְאִישׁ זָר – הָא אִם יֵשׁ לוֹ בֵּן, מִיתָה מַתֶּרֶת.
English: “The wife of the dead shall not be outside to a strange man” — this implies that if he has a son, death itself permits her to remarry.
On the daf / in context: The negative formulation teaches that only the absence of a son creates the prohibition of marrying an outsider; when a son exists, ordinary death frees her.
Derash from the negative formulation.
When the deceased leaves a son, the widow is free to marry any man; the restriction “not outside to a strange man” applies only when there is no offspring.