Deuteronomy 25:6

והיה הבכור AND IT SHALL BE THE FIRSTBORN … — It is the eldest brother who is to perform the duty of levirate marriage (Sifrei Devarim 289:1; Yevamot 24a). אשר תלד WHOM SHE WILL BEAR — This excludes from the operation of this law a sterile woman, since she cannot bear children (Sifrei Devarim 289:2). יקום על שם אחיו HE SHALL SUCCEED IN THE NAME OF HIS BROTHER — he who has married his (the deceased brother’s) wife shall receive the portion of the dead brother in his father’s property (Sifrei Devarim 289:3). ולא ימחה שמו THAT HIS NAME BE NOT WIPED OUT [OF ISRAEL] — thus excluding from the levirate marriage the wife of a castrate, whose name is anyhow wiped out (Sifrei Devarim 289:5; Yevamot 24a).

וְהָיָ֗ה הַבְּכוֹר֙ אֲשֶׁ֣ר תֵּלֵ֔ד יָק֕וּם עַל־שֵׁ֥ם אָחִ֖יו הַמֵּ֑ת וְלֹֽא־יִמָּחֶ֥ה שְׁמ֖וֹ מִיִּשְׂרָאֵֽל׃

And it shall be, that the firstborn which she bears shall succeed in the name of his brother who is dead, that his name be not wiped out in Yisra᾽el.