Considered to be particularly disorderly, they were the source of the most infamous Arab proverbs; and the butt of the most ferocious rants by Christian doctor and Baghdad theologian Ibn Buṭlān. According to him, owning these kinds of slaves was not easy. Judging them to be disobedient and fractious, he recommended they be treated with harshness and brutality and forced to work until they dropped to their knees. In his opinion, enslavement and hard labour went together because, he explained:
[T]heir extremely dark skin, hateful nature, mood swings, careless and unthinking temperaments, physical endurance and capacity to withstand pain and suffering predispose them "naturally" to hard labour. (Ibn Buṭlān, 1957, pp. 354-378)  
This treatise, written by the highly skilled practitioner Ibn Butlān, offers a singular and striking framework for psychological and social representation. The author tries to sketch a racialized classification of people and ethnicity. From this value grid he goes on to a kind of "rationalization" of domestic activity and socio-professional assignment. Armenians and Zanj, considered to be particularly disorderly and rebellious, are, from that moment on, described as the vilest and most dastardly of the enslaved, whether black or white, on planet earth.  
The recurrence of revolts, terrorism and repression led to the question of whether enslaved resistance boosted the impact of categorization. Indeed, we can see the gradual formation of the spectre of irremediable human inferiority of the enslaved. For their part, Muslim jurists did not fail to provide legal and moral assurances legitimizing the legality of the slave trade and reinforcing the authority of masters over their servants. In his Risäla, devoted to elements of Malikite Muslim dogma, Ibn Abī Zayd al-Qayrawānī (2005, pp. 146, 150, 182), while admitting ambiguity regarding enslaved status, did not hesitate to legally associate children born to enslaved females with cattle, and brown-skinned enslaved people with fleeing camels.