When the Muezzin calls the Iqaamah (second, small call to prayer) of the prayer, some fellow Muslims say 'La Ilaha Illa Allaah' in a loud voice. The Imaam objected to this, saying that this action does not belong to Islam and is not authentically proven to have been done by the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, or his Companions, may Allaah be pleased with them.
Out of respect for the Imaam, I did not argue with him concerning this subject. Hence, I hope that you would give me information about this point in order for the matters to be clear, since the Imaam has repeatedly rebuked those who say 'La Ilaha Illa Allaah' in the manner I that have mentioned. Is it really not recommended for a person to say 'La Ilaha Illa Allaah' (in this instance)?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

According to the Sunnah, the one who hears the Iqaamah should say the same words as the one who calls it, except when he says "Hayya ‘ala As-Salah" (Come to the prayer) and "Hayya ‘ala Al-Falah" (Come to success), after which one should say: "La Hawla wa la Quwwata illa billah" (There is no power nor strength save with Allaah). Also, when the one who calls the Iqaamah says: "Qad Qamat As-Salah" (i.e. The prayer is soon to be established), one should say: "Aqaamaha Allaahu wa Adaamaha" (May Allaah establish it and make it permanent).

Therefore, it is permissible to say ''La Ilaha Illa Allaah' while the Iqaamah is being called and there is no text in the Sharee'ah that entails prevention.

The Imaam has no right to object to whoever says so, unless the loud voices cause confusion for the people in the mosque. In this case, he should advise them to lower their voices to avoid confusing other worshippers.

Moreover, we advise all Muslims to verify religious rulings before issuing them, as this matter is greatly dangerous.

Allaah Knows best.