Quran 24:33

33 And let those who find not the means to marry be abstinent till God enriches them of His bounty. Those your right hands own who seek emancipation, contract with them accordingly, if you know some good in them; and give them of the wealth of God that He has given you. And constrain not your slave-girls to prostitution, if they desire to live in chastity, that you may seek the chance goods of the present life. Whosoever constrains them, surely God, after their being constrained, is All-forgiving, All-compassionate.