Muslim traders actually enslaved the Africans, with the help of African chiefs. Wish more blacks were aware of that.
This is pretty much a myth, as it applies to the Atlantic slave trade. Most slaves were sold directly to traders by pagan African chiefs, who controlled the entire coastline. Muslims were pretty much limited to the Sahel and Sudan, inland from the coast.
Muslims did, however, control the cross-Sahara and eastern Africa slave trade. These started earlier and continued longer than the Atlantic trade. The cross-Sahara trade, in particular, had a much higher death rate than the Atlantic trade.