Is it permissible to associate with a Muslim who frequents nightclubs, with the hope of changing him?

We advise approving a suitor of good religious commitment and character, based on the Prophet Muhammad’s (peace be upon him) saying: "If there comes to you one whose religious commitment and character you approve, then marry [your daughter] to him; otherwise, there will be tribulation on earth and widespread corruption." Since the marriage decision is five years away, you have ample time to approve someone more suitable. If no one comes, it is permissible to marry a relative as long as he is a Muslim.