Verses 22-25 of Chapter 4:

And do not marry at all those women whom your father had married though what has happened in the past is excepted. This is an indecent and abominable thing and an evil practice. Forbidden to you are your mothers, daughters, sisters, paternal aunts, maternal aunts, brother's daughters, sister's daughters, your foster mothers who have given a suckle to you, your foster sisters, who have taken suckle with you, the mothers of your wives, the daughters of your wives whom you have brought up, the daughters of those wives with whom you have had conjugal relations, but not of those wives with whom you have had no conjugal relations, and it is not sinful for you to marry their daughters (after having divorced them); and also forbidden to you are the wives of your sons who are from your loins, and it is unlawful for you to keep two real sisters as wives at one and the same time, hough what happened in the past is excepted, for Allah is indeed Forgiving, Merciful. And forbidden to you are the wedded wives of other people except those who have fallen in your hands (as prisoners of war): this is the Law of Allah that has been prescribed for you. With the exception of the above, it has been made lawful for you to seek in marriage with your wealth any other women provided that you keep them in wedlock and not in licentiousness. Then you should pay them their dowries as an obligation for the enjoyment of conjugal relations with them. However, there is no harm if a compromise is made in the dower by mutual consent after an agreement about it; Allah is All-Knowing, All Wise. Whoever cannot afford to marry free Muslim women, should marry one of the Muslim slave-girls in your possession; Allah has full knowledge of your Faith. You all belong to one and the same community; therefore, you may marry them with the permission of their guardians and give them their fair dowries so that they may live a decent life in wedlock and not in licentiousness nor may have secret illicit relations. Then if they are guilty of indecency, after they have been fortified by wedlock, they shall be given half the punishment prescribed for free women. This concession has been made for those of you who might apprehend a moral lapse without marriage, but it is better for you to practice self-restraint, and Allah is Forgiving, Merciful.