Is it permissible for a friend who frequents houses of ill repute to claim that hiring a prostitute falls under the category of "what your right hand possesses"? And is his prayer invalid because it does not deter him from indecency and evil?

A person cannot be described as committed to their religion while frequenting places of vice and committing immoral acts such as fornication (zina), based on the Prophet Muhammad’s (peace be upon him) saying: "The fornicator does not commit fornication while he is a believer." Allah the Almighty has stated that fornication multiplies the torment on the Day of Judgment, except for those who repent, believe, and do righteous deeds. The claim that this relationship is permissible under the pretext of 'milk al-yamin' (what your right hand possesses) is false, as Islam has forbidden selling a free person and the price of a harlot. The prayer of a disobedient person, if it fulfills its conditions and pillars, is valid and does not require repetition. True prayer indeed prohibits indecency and evil, as stated in the Quran.