What is incumbent upon someone who speaks loudly in the mosque during prayer and disturbs the worshippers, and how can he be politely restrained after being advised kindly and failing to respond?

Raising one's voice and causing disturbance in the mosque is forbidden by religious law (Sharia), based on the Prophet's (peace be upon him) saying: "Beware of the commotions of the markets," and his saying: "Let not some of you raise their voices over others with the Quran." If raising one's voice with the Quran is prohibited, then doing so with Hadith or other matters is even more so. Whoever does this should be advised gently and privately. If he refuses and persists, people are permitted to remove him from the mosque if he is causing them harm. Some scholars have issued a fatwa to this effect. However, it is preferable to report the matter to the competent authorities to avoid greater harm.