What is the ruling on the prayer of the congregants and the imam in a mosque where there is a slight echo of the transitional takbeers or the saying of "Sami' Allahu liman Hamidah" (Allah hears him who praises Him)? And does the validity [of the prayer] differ with or without the repetition of the echo, knowing that this is the closest mosque to the questioner?

If the echo device causes letters to reverberate in the mosque, its system must be adjusted; because that is an addition to the words of Allah and likens it to melodious songs. Ibn 'Uthaymeen issued a fatwa prohibiting the echo because it adds to the Qur'an what is not from it, and makes the letter repeat several times, which does not increase devotion but rather aversion. Therefore, the Imam must advise the worshippers and immediately disconnect the echo wire. The prayer is not invalidated by the presence of the echo as long as the worshipper has recited the Fatiha completely, and the repetition of some letters does not change the meaning of the Qur'an. There is no harm in praying in this mosque, but if the echo affects your devotion, it is better to pray in another mosque where your devotion increases.