What is the ruling on saying "Ameen" aloud behind the Imam in a loud prayer and in the Friday supplication, and is it true that the Prophet, peace and blessings be upon him, said: "Whoever says to his brother: 'Be quiet,' then there is no Jumu'ah for him"?

Scholars have differed regarding the permissibility of raising one's voice with "Ameen" behind the Imam in audible prayers. The majority holds it to be permissible, while others believe it is sunnah (definition) to say it silently. The majority relied on the hadith (definition) of the Prophet, peace be upon him: "Ameen" and he raised his voice with it, and on his command to say "Ameen" when the Imam says "Ameen."

As for saying "Ameen" during the Friday sermon for the Imam's supplication, the prescribed way is for it to be silent, such that the worshiper hears only himself, and does not say it aloud. This "Ameen" is not among the forbidden speech during the sermon.