All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
First of all, we congratulate this man and that woman on their repentance to Allah, the Exalted, and ask Him, the Almighty, to preserve their religion for them and to increase them in guidance and righteousness.
As for the ruling on the fornicator’s marriage to the woman with whom he had fornication before repenting, scholars differed in opinion over it, as follows: some of them are of the view that it is valid while some others are of the view that it is invalid. It is actually an issue that is based on ijtihaad (scholars’ personal reasoning), which means that it is allowed to work according to the opinion of those who view the validity of marriage, especially if we take into account the fact that the husband has already consummated the marriage contract with that woman and that she had delivered him a child.
Allah knows best.