Assalaamu alaykum. My question is the following: what is the ruling on the marriage in which a man pays dowry and has intimate relations with the girl before they get married. Is the dowry given affected by the intimate relations that they have. Must he give another dowry and repeat the marriage?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

If you mean that this man has not concluded the marriage contract yet, but agreed with this woman on paying her the dowry and had intimate relations with her, then you should know that this is not considered a dowry, rather, this is prostitution, and they have committed adultery; may Allaah safeguard us. If this dowry was given to the woman in return for illicit intercourse, then it must not be returned to the man; as the person should not acquire both the unlawful benefit and the money that he has paid for it. Also, the woman does not have the right to use it. Instead, it must be offered in charity for the benefit of the poor and needy.

Shakhul-Islam Ibn Taymiyyah wrote, “...in this case he cannot be given the right to the unlawful benefit and the compensation that he has already paid for it. Instead, it should be spent in charity for the benefit of Muslims. The same applies to the fees of a prostitute and fortuneteller and the like of the compensation paid for a defect or in return for an unlawful benefit if the sinner has consumed the compensation...” [Al-Fataawa Al-Kubra]

It is incumbent on this man to repent to Allaah of committing adultery; verily, it is a serious sin about which Allaah made stern warnings in the worldly life and the Hereafter.

However, it is permissible for him to marry this woman after her repentance and istibraa' (i.e. giving birth if she is pregnant or observing a waiting period of three menses according to one view of the scholars, or one menses according to another view). However, if he has concluded the valid marriage contract, then he should pay her dowry unless the payment he had given her earlier was not in return for illicit intercourse and was given to her as the dowry. In this case, she has received her dowry and he is not obliged to pay her another dowry unless he willingly chooses to do so.

We have underlined the conditions of a valid marriage in Islam in fatwa 83629. We have also emphasized that it is prohibited for the Muslim woman to establish any relationship with a non-mahram (marriageable) man outside of marriage in fatwa 81356. The sharee'ah-acceptable factor in this regard is to conduct a valid marriage contract and not a mere engagement or marriage proposal to a woman or to her guardian.

Allaah knows best.