Bereishis Rabbah 94:3.
Sefaria — Bereishis Rabbah 94:3
וַיֹּאמֶר יִשְׂרָאֵל רַב, רַב כֹּחוֹ שֶׁל יוֹסֵף בְּנִי, שֶׁכַּמָּה צָרוֹת הִגִּיעוּהוּ וַעֲדַיִן הוּא עוֹמֵד בְּצִדְקוֹ הַרְבֵּה מִמֶּנִּי.
English: “And Israel said, ‘Rav’” — great is the strength of my son Joseph: many troubles befell him, yet he remained righteous, more than I did.
What Is Learned: The midrash turns “rav” into an acknowledgment of Yosef’s steadfast righteousness under suffering.