The statement is true. In the Muslim societies, or rather Caliphates and empires, the slaves were traded just like the other goods. The slaves varied in ethnicity, race, culture, religion. The Muslim kept and sold as slaves the people that were captured in war. The ones that refused to accept their religion were also often enslaved and sold as slaves throughout their territory. There were slaves from Western Asian origin, from European origin, African origin, and they were all treated as not worthy of leaving, and that the only thing that they were partially good at was to serve and work for the Muslims.
