Ruling on reciting adhkaar out loud in unison

Firstly: 

Dhikr in
general, if it involves raising the voice and reciting in unison, is a
bid‘ah (innovation) that has been introduced into the religion and was not
the practice of the righteous early generations. 

Ash-Shaatibi
(may Allah have mercy on him) said: 

If there is
a text that encourages people to recite particular phrases of dhikr, and
some people commit themselves to gathering to recite dhikr in unison, or at
a certain time that is singled out from all other times, then we should note
that although these phrases were referred to in a shar‘i text by way of
encouraging people to say them, there is nothing in that to indicate this
particular way and time of doing it. Rather in that text there may be
something to indicate the contrary, because adhering to something that is
not binding in Islam may give the impression that this is part of the
religion, especially if it is done by leading figures who are regarded as
setting examples in places where people gather, such as the mosque. 

Therefore
the early generation did not commit to doing such things and it is more
appropriate for them to have done those actions if they were prescribed in
Islam. But dhikr in general is something that is Islamically prescribed in
many situations, unlike other acts of worship, and this du‘aa’ is dhikr or
remembrance of Allah, yet the salaf did not adhere to a particular manner of
doing it or limit it to specific times, such that this dhikr is connected to
those particular times, unless there is evidence for a particular time, such
as morning or evening. And they did not say it out loud unless the shar‘i
text indicated that it should be said out loud, such as the dhikr on the two
Eids and the like. With regard to dhikrs other than that, they persisted in
hiding it and said it privately (not out loud). Hence when the Sahaabah
raised their voices in du‘aa’, the Prophet (blessings and peace of Allah be
upon him) said to them: “Be easy with yourselves (and lower your voices),
for you are not calling on one who is deaf or absent,” and so on. And they
did not recite out loud or in unison. 

Everyone who
goes against this principle has gone against the fact that the text is
general in meaning and does not restrict it to a particular time, because
the one who does that has restricted it on the basis of his own opinion and
has gone against those who had better knowledge of Islam than him, namely
the righteous early generations (the salaf – may Allah be pleased with
them). End quote. 

Al-I‘tisaam,
1/188-189 

Shaykh
al-Islam (may Allah have mercy on him) was asked about a man who established
a waqf and in some of his conditions he stipulated that they should recite
whatever they are able to (of Qur’aan) and recite Subhaan Allah
(Glory be to Allah), Laa ilaaha ill-Allah (there is no God but Allah)
and Allahu akbar (Allah is most great), and send blessings upon the
Prophet (blessings and peace of Allah be upon him) after Fajr until sunrise.
Is it better to do that out loud or quietly? 

He replied: 

Rather it is better to recite dhikr and du‘aa’ – such as sending
blessings upon the Prophet (blessings and peace of Allah be upon him) –
quietly, unless there is a reason to do otherwise. At this particular time
it is especially preferable (to recite it quietly), because Allah says
(interpretation of the meaning): “And remember your Lord by your tongue
and within yourself, humbly and with fear without loudness in words in the
mornings” [al-A‘raaf 7:205]. And in as-Saheeh it is narrated from
the Prophet (blessings and peace of Allah be upon him) that when he saw the
Sahaabah (may Allah be pleased with them) raising their voices in dhikr, he
said: “O people, be easy with yourselves (and lower your voices), for you
are not calling on one who is deaf or absent; rather you are calling upon
One Who is All-Hearing and Close. The One upon Whom you are calling it is
closer to one of you than the neck of his mount.”

End quote
from al-Fataawa al-Kubra, 4/246 

The scholars
of the Standing Committee said: 

Dhikr in
unison is an innovation (bid‘ah) because it is something that has been
introduced into the religion. The Prophet (blessings and peace of Allah be
upon him) said: “Whoever introduces something into this matter of ours that
is not part of it will have it rejected.” And he (blessings and peace of
Allah be upon him) said: “Every newly invented matter is an innovation, and
every innovation is going astray.” What is prescribed is to remember Allah,
may He be exalted, without reciting in unison.

End quote.
Fataawa al-Lajnah ad-Daa’imah, 24/268 

Secondly: 

It is more
makrooh (disliked) to raise the voice in reciting dhikr and du‘aa’, and to
recite in unison, if that could annoy other people who are praying or
offering du‘aa’ or remembering Allah (dhikr). 

It was
narrated from ‘Abdullah ibn ‘Umar (may Allah be pleased with him) that the
Prophet (blessings and peace of Allah be upon him) observed i‘tikaaf and
addressed the people, saying: “When one of you stands to pray, he is
conversing with his Lord, so let each of you think of what he is saying to
his Lord, and no one among you should raise his voice over anyone else when
reciting in the prayer.”

Narrated by
Ahmad, 4909; classed as saheeh by al-Albaani. 

Shaykh
al-Islam Ibn Taymiyah (may Allah have mercy on him) said: No one should
raise his voice in recitation in such a way that he annoys others, such as
other worshippers.

End quote.
Majmoo‘ al-Fataawa, 23/61 

Thirdly: 

With regard
to the report narrated by Muslim (2701) from Mu‘aawiyah ibn Abi Sufyaan (may
Allah be pleased with him), according to which the Messenger of Allaah
(blessings and peace of Allah be upon him) came out to a circle of his
companions and said: “Why are you sitting here?” They said: We are sitting
to remember Allaah and praise Him for having guided us to Islam and blessed
us with it. He said: “By Allaah, are you only sitting for that purpose? They
said: By Allaah, we are only sitting for that purpose. He said: “I did not
ask you to swear because I am accusing you, but Jibreel came to me and told
me that Allaah was boasting of you to the angels.” 

And the
report also narrated by Muslim (2699) from Abu Hurayrah (may Allah be
pleased with him) who said: The Messenger of Allah (blessings and peace of
Allah be upon him) said: “No people gather in one of the houses of Allaah,
reciting the Book of Allaah and studying it together, but tranquillity will
descend upon them, mercy will overshadow them, the angels will surround them
and Allaah will mention them to those who are with Him.” 

–There
is nothing in these reports to suggest that dhikr should be recited in
unison.

Shaykh Ibn
‘Uthaymeen (may Allah have mercy on him) said: 

The correct
view concerning this matter is that the two hadeeths refer to those who
study the Book of Allah together and recite it. Similarly, with regard to
people who are remembering Allah, it is general in meaning and should be
understood in the light of other, specific reports that describe the way in
which dhikr was done at the time of the Prophet (blessings and peace of
Allah be upon him) and his Companions. It was not known among them that they
would remember Allah, may He be exalted, by reciting dhikr in unison or that
they read or recited the Qur’aan in unison. The phrase “studying it
together” indicates that this studying together is done one after another.
Either one reads, and when he has finished the next one reads the same text,
and so on; or each one of them reads one part, and the next one reads from
where the first one stopped. This is the apparent meaning of the hadeeth.
With regard to the other hadeeth in which it says that they remembered
Allah, we say the same thing: it is general in meaning and should be
understood in the light of the texts that speak of the specific way in which
dhikr was done at the time of the Prophet (blessings and peace of Allah be
upon him) and his Companions. It was not known among them that they would
get together and recite dhikr in unison. 

End quote.
Fataawa Noor ‘ala ad-Darb by Ibn ‘Uthaymeen, 19/30 

For more
information please see the answer to question no.
10491 

And Allah knows best.