What are the rulings concerning an invalid marriage, and what are its implications?

A فساد (irregular) marriage is one that lacks a condition for a valid marriage. Whoever enters into it knowingly of its irregularity is sinful, shall be disciplined, and separated from his wife. There is no prescribed punishment for him due to the scholarly disagreement regarding the validity of such marriages. Rather, he is to be disciplined for committing an act that is unlawful, but for which there is neither a prescribed punishment nor expiation. If he has consummated the marriage, the mahr (dower) is established for her, and the children are attributed to their father and inherit from both him and their mother.