וַיֹּ֕אמֶר לֹֽא־יֵרֵ֥ד בְּנִ֖י עִמָּכֶ֑ם כִּֽי־אָחִ֨יו מֵ֜ת וְה֧וּא לְבַדּ֣וֹ נִשְׁאָ֗ר וּקְרָאָ֤הוּ אָסוֹן֙ בַּדֶּ֙רֶךְ֙ אֲשֶׁ֣ר תֵּֽלְכוּ־בָ֔הּ וְהוֹרַדְתֶּ֧ם אֶת־שֵׂיבָתִ֛י בְּיָג֖וֹן שְׁאֽוֹלָה׃
야곱이 가로되 내 아들은 너희와 함께 내려가지 못하리니 그의 형은 죽고 그만 남았음이라 만일 너희 행하는 길에서 재난이 그 몸에 미치면 너희가 나의 흰 머리로 슬피 음부로 내려가게 함이 되리라
Rashi
לא ירד בני עמכם MY SON SHALL NOT GO DOWN WITH YOU — He did not accept Reuben’s offer. He said, “What a fool is this oldest son of mine! He suggests that I should kill his sons. Are they his only and not mine also?” (Genesis Rabbah 91:9)
Chizkuni
וקרהו אסון, “and some mishap would befall him;” the letter ו in the word קרהו has the vowel shuruk, whereas the letter ק has the semivowel sh’va.
Sforno
My son. Yaakov refers to Binyamin in this way because he was the only son left from his primary wife [Rochel].