It is narrated from Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with them both) that the Noble Prophet (peace and blessings be upon him and his family) forbade the meat of domestic donkeys and from the jallalah animal, from riding it and from eating its meat.
Hadith Referenceالفتح الربانی / كتاب الأطعمة / 7335
Benefits: ... "Jallalah" refers to that animal which consumes such an amount of filth and impurity that the impurity permeates its being, and a distinct foul odor begins to emanate from it. Its meaning, therefore, is that impurity has become predominant in this animal, and such an animal, due to this impurity, will be unlawful (haram). Its sweat will also become impure (najis). If such an animal later ceases to eat impure things and the effects of impurity are completely removed from its body, then it will become lawful (halal), meaning the fundamental issue is that of impurity.