Collective and aloud Dhikr assemblies
The hadith qudsi already mentioned - "Those who remember Me in an assembly..." - makes collective dhikr, aloud, the gateway to the fulfillment of God's promise:
Remember Me and I will remember you.
It is no wonder that such assemblies receive from God and His Prophet (may the peace and blessings of God be upon him) the highest praises and blessings, as evidenced by many excellent and authentic hadiths.
According to bukhari and muslim, the Prophet (may the peace and blessings of God be upon him) said that God asks His angels to travel the roads to find the people of dhikr, that is to say those who say lâ ilâha illâ llâh and similar expressions, and when they found a group of people (qawm) who say the dhikr, they call each other and they wrap them in successive levels up to the first heaven, which is located in the knowledge of God. This means that an unlimited number of angels stand above the group. It does not say: "when they have found a person...", which proves that being a group to practice dhikr is a plus for obtaining this particular reward.
God asks His angels (in fact, He already knows, but it is to make it all understandable to us): "What do My servants say?" He does not say "servant" but `ibadi, "servants", in the plural. The angels say: "They praise You (tasbih), magnify Your name (takbir) and glorify You (tahmid), giving You the best attributes (tamjid)". Can this be considered a lesson, or group study? Can we say that it is silent? Is it not rather to say "alhamdu lillah" or other similar formulas?
God says, "Have they seen Me?" The angels answer, "O our Lord, they have not seen You!" He says, "They praise Me when they have not seen Me. if they had seen Me?" The angels replied, "O our Lord, if they had seen You, they would do more and more acts of worship, they would do more and more tasbih, more and more takbir, more and more tamjid!”
God said, "What are they asking?" The angels said, "They are asking for Your Paradise!" He said, "Have they seen Paradise?" They replied, "O our Lord, they have not seen it!" He said, "How would they be if they had seen him?" They replied, "They would be even more attached to him and attracted to him!"
God says, "What do they fear and what do they turn away from?" (When we say ya ghaffar - O You who forgive - or ya sattar - O You who are silent - it means that we fear Him because of our sins , that we ask Him to hide our sins and forgive us) The angels said: "They fear the fire of hell and they turn away from it!" He said: "Have they seen the fire of hell? "They answered, 'O our Lord, they have not seen the fire of hell!' He said, 'How would they be if they had seen the fire of hell?' they had seen the fire of hell, they would move further and further away from it, and they would be even more afraid of it!”
Listen carefully to what follows. God says, "I call you to witness (Does God need witnesses? He doesn't need them because He said, 'God is sufficient as a witness.' Why make angels witnesses? God changes- Is He of the opinion? "I take you to witness" means here "I assure you") that I have forgiven them" (And why did God forgive them? Because, as the beginning of the hadith, it is about a group of people who together recite the names of God and remember Him by His dhikr). One of the angels said: "O my Lord, among them was someone who did not belong to their group, but who was there for some reason" (this person was there for another reason, for example to ask something to someone). God says, "They are such a group that whoever sits down with them - no matter for what reason - will also have their sins forgiven."
In his book miftah al-janna (translated by mostafa badawi, Key to the garden, Quilliam Press, p. 107-108), imam ahmad mashkur al-haddad says:
This hadith specifies the merits that reside in the assembly of dhikr, for each of those who are present and who practice dhikr aloud and in unison. Phrases like "they call upon Thee" (plural), and "they are the people who sit down" refer to those who come together to remember and do so in unison, which can only be done 'out loud. One whose dhikr is silent does not need to participate in a meeting with other brothers.
This is developed in the following hadith qudsi. God says (Bukhari and Muslim):
I am for My servant what he expects Me to be. I am with him when he remembers Me. If he remembers me