A donkey remains a donkey / Never went out an ass and came home a horse
Figuratively: a fool cannot become wise. "If someone is stupid, it lasts a long time."
(Modern Hebrew)
Translation
Expression (Hebrew)
חֲמוֹר נִשְׁאָר חֲמוֹר
Definition (Hebrew)
בְּהַשְׁאָלָה: טִיפֵּשׁ אֵינוֹ יָכוֹל לְהֵיהָפֵךְ לְחָכָם. "אִם מִישֶׁהוּ טִיפֵּשׁ-זֶה לְהַרְבֵּה זְמַן".
(הָעִבְרִית הַחֲדָשָׁה)