What is the ruling on a man who married with lawful and unlawful money, then regretted it and realized that he had married with unlawful money, and what is incumbent upon him to do?

The marriage is valid as long as it has met the Shariah conditions. The fact that the mahr (dowry) came from ill-gotten gains does not harm the validity of the marriage. The husband must repent and return the ill-gotten money to its rightful owners, or give it away as charity on their behalf if he is unable to return it.