Those who cannot find a match, must maintain morality. They should wait until God showers them out of His Grace. As for those slaves of yours who wish to be free and then marry (and you find them responsible people), grant them their freedom; also give them some capital out of what God has given you at first place. Do not force your female slaves into prostitution so that you make a little bit money. If the female slaved are forced to do so, God will forgive them as He is the Most Forgiving, the Most Merciful.