Is it permissible for me to propose to a girl who is engaged to a man who does not pray, smokes, and drinks alcohol, despite the Prophet's (peace and blessings be upon him) prohibition against proposing over a Muslim's engagement?

It is forbidden to propose to an engaged woman after the engagement has been confirmed, unless the first suitor is an open sinner (fasiq). In this case, it is permissible to propose to her if the second suitor is a person of religious commitment and good character, because an open sinner has no sanctity. One who abandons prayer, drinks alcohol, and smokes is considered an open sinner. As for the ruling on a girl marrying such a person, if he abandons prayer out of laziness, her marriage to him is invalid according to those who deem the one who abandons prayer to be a disbeliever. However, according to those who say that abandoning prayer is a grave sin but not disbelief, there is a difference of opinion among scholars regarding the validity of marriage to an open sinner, and whether it must be annulled or if it is valid despite the sin, with many Maliki scholars favoring the annulment.