Or HaChaim on Genesis 38:1/אור החיים על בראשית ל״ח:א׳

138.1. וירד יהודה מאת אחיו, Yehudah descended and turned from his brothers, etc. Our sages in Sotah 13 say that the brothers demoted him. Ibn Ezra says that anyone who comes from the northern part of the world to the South is considered as "descending." What he said is correct; it does not apply here, however, because then the Torah need not have added: "from his brothers." This clearly indicates that Yehudah's descent, i.e. demotion, was caused by his brothers. It also says: ויט עד איש, "he turned to a certain person, etc." Our sages are quite correct when they interpret the word וירד as a moral descent and the words ויט, etc., are integral to the verse.