Many of the Muslims enslaved in the Mediterranean were enslaved by Arabs. These were then taken into slavery in the Middle East.

However, many Muslim Africans were taken from West Africa and enslaved in the Americas. In Servants of Allah, Sylviane Diouf talks about it. She talks as well about how the Spanish ensured that their slaves had been converted prior to being brought to the New World specifically to ensure that they were not spreading non-Catholic faiths. There were also some efforts made in US slavery to convert Muslim slaves, though this varied. Estimates are that roughly 10% of American slaves were Muslim, though this figure is nigh-on impossible to know for sure. What's interesting is that some of the Muslim slaves who were perceived to be educated and intelligent were said to not be Africans, and were instead Moors or Arabs, despite the fact that they were as much from Africa as their brethren. Largely, the type of Islam practiced by enslaved Africans has been lost due to forced conversion or the harshness of slavery, but the Nation of Islam still pays homage to it, sometimes calling conversions "reversions" and drawing a tradition back to it.

It's not quite what you're looking for, I think, but I hope you find my answer interesting anyway. :)