“Islam required that slaves should be treated kindly and encouraged freeing slaves”  p462 My World History(Early Ages)

“Allah sets forth another Parable of two men: one of them dumb, with no power of any sort; a wearisome burden is he to his master, whichever way he directs him, he bring no good: is such a man equal with one who commands Justice, and is on a Straight Way?”  Quran 16:76

“O Prophet! We have made lawful to thee thy wives to whom thou hast paid their dowers; and those (slaves) whom thy right hand possesses out of the prisoners of war whom Allah has assigned to thee”   Quran 33:50

In Mecca, before Muhammad began Islam, he had one slave a gift from his wife and set him free. In Medina, after Muhammad began Islam, he had over 50 slaves, and traded many slaves in his life-time. What adds up? Do the math. Know the truth.