4:25

If any of you cannot afford to marry a free believing woman, let him marry one of his own slave girls who is a believer; Allah knows how good you are in your faith. You all belong to one and the same community. Marry them with the permission of their family and give them their fair dowry so that they may live a decent life in wedlock and not live as prostitutes or look for secret illicit relationships. Then if after marriage they commit adultery, they shall be given half the punishment prescribed for a free adulteress. The concession of such a marriage is for those of you who fear that they might commit a sin if they do not get married, but it is better for you to practice self-restraint. Allah is Forgiving, Merciful.