The prophet SAW did have slaves and he freed them. His blessed companions also had slaves and they freed many. Yes you are right slaves were acquired either from war or they were born into it. Islam removed the avenue of slavery which they used to do which was to capture free men.I dont believe nabi mohamed had slaves and i think islam didnt entercourage to go and take civilians as slave the only slavery tht is allow is when muslims army goto war and win then take non muslims army mans