What is Islam's view on the dowry (mahr)? Is it permissible or forbidden? And if it is forbidden, what should one who has taken it do?

The dowry in Islam is a right of the wife, and Allah has commanded that it be given to her with a willing heart, and He has forbidden taking anything from it except with her consent. The dowry must be paid in full, even if it is a qintar (large amount) of wealth, in exchange for what has been made lawful from the wife, which is the firm covenant that took place between the spouses. It has been mentioned in the Prophetic Sunnah that the dowry is obligatory for the wife.