An-Nisa · 4:24

24. Those who are already married are prohibited to you, except those who you have captured whilst fighting in Allah’s cause: they are allowed to you after making sure they are not pregnant – this is what Allah has decreed. All women other than those who have been prohibited are allowed for you, if you seek them with your wealth, in a chaste way, desiring what is lawful and not desiring sexual immorality. Give those you enjoy in marriage their dowry, which Allah has made an obligation on you. However, there is nothing wrong if you mutually agree, after the obligation of the dowry has been set, to increase it, or to give up part of it. Allah knows His creation and nothing about them is hidden from Him. He is Wise in His administration and in His sacred law-giving.