What is the ruling on one who always prays in congregation but utters obscene words with his friends, and how can one avoid bad company?

Allah Almighty rewards obedience and punishes disobedience. As for one who maintains congregational prayer but speaks impermissibly, there is hope for him in the reward for his prayer, but there is fear for him of punishment due to his speech. He should be advised to refrain from indecency, for the Prophet, peace and blessings be upon him, said: "The believer is not a slanderer, nor a curser, nor an indecent person, nor an obscene one," and he also said: "Indeed, Allah does not like indecency and obscenity." His prayer is not invalidated unless his speech is among that which the Sharia has deemed invalidating. To avoid bad company, one must keep away from mixing with them, sitting with them, and accompanying them, just as one avoids an infectious patient.