Zikr in Assembly
The following ahadith is about those Sahaba who did zikr in assembly and in a circle, and were praised by the Messenger of Allah (Allah bless him and give him peace) for it:
Hadhrat Abu Sa`eed Khudri relates that once Hadhrat Mu`awiyah visited the mosque and saw a circle (of reciters). He asked,
"What has made you sit?"
They said, "We have assembled here to remember Allah."
He [Mu`awiyah] said, "By Allah you did not sit except for this purpose?"
They affirmed, "We did not sit except for this."
Hadhrat Mu`awiyah then told them, "I did not ask you to swear on account of any malice. None of you can match me for scanty narration of the Messenger of Allah (Allah bless him and give him peace) (and as such have narrated very few traditions about him). The Messenger of Allah (Allah bless him and give him peace) once visited a gathering of his companions and inquired, `
What has made you assemble here?'
They answered, `We have gathered to remember Allah and praise Him for having led us to Islam and granted this favour to us.'
The Messenger of Allah (Allah bless him and give him peace)nquired, `Do you affirm by Allah that it is so?'
The Messenger of Allah (Allah bless him and give him peace) Companions affirmed, `By Allah we are sitting here for this purpose only.'
He [the Prophet (Allah bless him and give him peace)] said, `I have not put you on oath on account of any doubt, but angel Jibreel had visited me and told me that Allah felt proud of you among the angels.'"
[From Sahih Muslim, and also in the Riyadh us-Saliheen of Imam Nawawi.]
Here is another hadith, which shows the benefit of doing dhikr in assembly.
Ibn `Umar reported, "The Prophet, peace be upon him, said,
`When you pass by a garden of paradise, avail yourselves of it.' The Companions asked, `What are the gardens of Paradise, O Messenger of Allah?" The Prophet, peace be upon him, replied, `The assemblies of zikr. There are some angels of Allah who go about looking for such assemblies of zikr, and when they find them they surround them.'"
[Quoted from Fiqh us-Sunnah compiled by As-Sayyid Sabiq, vol. 4, ch. 6.]
There is also this important hadith about zikr in general, and zikr in an assembly:
On the authority of Abu Hurayrah (may Allah be pleased with him), who said that the Prophet (may the blessings and peace of Allah be upon him) said: Allah the Almighty says:
I am as My servant thinks I am. I am with him when he makes mention of Me. If he makes mention of Me to himself, I make mention of him to Myself; and if he makes mention of Me in an assembly, I make mention of him in an assembly better than it. And if he draws near to Me a hand's span, I draw near to him an arm's length; and if he draws near to Me an arm's length, I draw near to him a fathom's length. And if he comes to Me walking, I go to him at speed.
[It was related by al-Bukhari, and also by Muslim, at-Tirmidhi and Ibn Majah. From "Forty Hadith Qudsi," selected and translated by Ezzeddin Ibrahim and Denys Johnson-Davies (Dar Al-Koran Al-Kareem, Lebanon, 1980), hadith no. 15.]