9:12ט׳:י״ב
1 א

לדרת עולם. נִכְתַּב חָסֵר, שֶׁיֵּשׁ דּוֹרוֹת שֶׁלֹּא הֻצְרְכוּ לְאוֹת לְפִי שֶׁצַּדִּיקִים גְּמוּרִים הָיוּ, כְּמוֹ דּוֹרוֹ שֶׁל חִזְקִיָּהוּ מֶלֶךְ יְהוּדָה וְדוֹרוֹ שֶׁל רַבִּי שִׁמְעוֹן בֶּן יוֹחַאי (ב"ר):

לדרת עולם FOR GENERATIONS FOR EVER — The word לדרת “for generations” is written defective (without Vav) (implying that the sign will be necessary only for such generations as are “defective’’ in faith) because there will be some generations which will require no sign since they were completely righteous, such as the generation of Hezekiah, king of Judah, and the generation of R. Simeon ben Yochai (Genesis Rabbah 35:2).