Praise be to Allah, the Lord of the Worlds.

Dhikr and Du`aa (Remembering Allah and Supplicating to him) are amongst the greatest acts of devotion that bring a Muslim closer to Allah. As known to all, their virtue is attested to by many texts of Sharia(Quran and Sunnah).As agreed upon by all scholars, through both of these acts, a Muslim declares being a slave of Allah, the Almighty, and seeks to draw nearer to Him. Thus, Allah honors him for that, helps him and answers his prayers. He the Exalted says{what means}, "Therefore remember Me, I will remember you. Give thanks to Me, and reject not Me."{al-Baqarah, 152}. He the Almighty also says{what means}, "And your Lord hath said: Pray unto Me and I will hear your prayer. Lo! those who scorn My service, they will enter hell, disgraced."{Ghafir, 60}. As for offering congregational Dhikr and Du`aa loudly, many texts of Sharia indicate that it is Mustahab{Recommended}. For example, the aforementioned verses in which the addressees are asked to remember Allah and make supplication to Him in the plural form. From the Prophetic Sunnah, we give the following examples: Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (PBUH) said, "Allah the Exalted says: 'I am as my slave expects me to be, and I am with him when he remembers Me. If he remembers Me inwardly, I will remember him inwardly, and if he remembers Me in an assembly, I will remember him in a better assembly (i.e., in the assembly of angels)."[Al-Bukhari and Muslim]. Abu Hurairah and Abu Sa'id Al-Khudri (May Allah be pleased with them) reported: The Messenger of Allah (PBUH) said, "When a group of people assemble for the remembrance of Allah, the angels surround them (with their wings), (Allah's) mercy envelops them, Sakinah, or tranquillity descends upon them and Allah makes a mention of them before those who are near Him."{At-Tirmithi}. As known to all, congregational Dhikr is delivered loudly.However, based on texts of Sharia, some scholars concluded that it is also recommended  to offer Dhikr and D`uaa silently and there is no contradiction between this view and the earlier. This is because recommending that Dhikr and D`uaa are delivered loudly  in congregation or individually, or recommending offering them silently varies depending on persons and circumstances. Thus, it isn`t permissible to consider the one who adopts any of these two opinions as mistaken or Mubtadi`(innovator).As regards the situations where a special Dhikr or Du`aa was reported, it is better to adopt what is given in the Prophetic Sunnah, such as the remembrances and supplications of prayer. However, remembrances and supplications that aren`t based on evidence from the Prophetic Sunnah go under the general meaning of the above verses and narrations.Many texts of Sharia show that Dhikr is a means of lifting affliction. For example, narrated Anas ibn Malik: The Prophet (PBUH) used to say: "O Allah, I seek refuge in Thee from leprosy, madness, elephantiasis, and evil diseases."{Ahmad & Abu Dawoud}. Had this been useless, the Prophet(PBUH) wouldn`t have taught it to us. This is in addition to several narrations which teach seeking refuge with Allah from poverty, worry and grief. As for making groups for seeking Allah`s forgiveness, supplications and fasting, they all fall under helping one another in piety and righteousness as reflected in the verse where Almighty Allah says{what means}, "  Help not one another unto sin and transgression"{al-Ma`ida, 2}.Moreover, this  isn`t considered an innovation(Bid`ah) because, from the view point of Sharia,  every new matter that contradicts Sharia is a Bid`ah, and this gathering is a means to an act of worship(Dhikr & Du`aa) not an act of worship in itself. But, from the view point of language, every new matter is called a Bid`ah regardless of whether it contradicts Sharia or not. In his book entitled {Jami` al-Ulum waal Hikam}, Ibn Hajar said, "Bid`ah refers to every new matter that has no origin in Sharia since that which has an origin in Sharia isn`t a Bid`ah, even if it is a Bid`ah in terms of language." And Allah the almighty knows best.