Remembrance of Allah (Dhikrullah) should be a part of all our gatherings:

 A Muslim always remembers Allah, whether he is alone or in a gathering. 
There are many Ahadeeth that stress that Remembrance of Allah (Dhikrullah) should be a part of all our gatherings and meetings.

The Prophet ﺻﻠﯽ الله ﺗﻌﺎﻟﯽٰ ﻋﻠﯿﮧ ﻭﺍٓﻟﮧ ﻭﺳﻠﻢ  said, "Whoever sits and does not mention the Name of Allah (before he rises) will find it a cause of sorrow from Allah. Whoever lies down to sleep and does not mention the name of Allah before rising, will find it a cause of sorrow from Allah." - Abu Dawud 4/264, Al-Jami' As-Saghir 5/342 (Sahih).

Abu sa’id رضي الله ﺗﻌﺎﻟﯽٰ عنه  narrated that the Prophet ﺻﻠﯽ الله ﺗﻌﺎﻟﯽٰ ﻋﻠﯿﮧ ﻭﺍٓﻟﮧ ﻭﺳﻠﻢ  said,

“ Whenever a group gathers and does not remember Allah during their meeting, it will incur sorrow on them on Judgement Day, even if they enter the Garden”

(An-Nasa’ee in As-Sunan Al-Kubra, Kitab ‘amal Al-Yawm Wal-Laylah (Book of Actions done in the Day and Nights) no.10242)

Ibn `Umar (May Allah be pleased with them) reported: "The Messenger of Allah (PBUH) seldom left a gathering without supplicating (doing Dua)..." [Tirmidhi with a Hasan chain]. 

 وعن أبي هريرة رضي الله عنه قال قال رسول الله صلى الله عليه و سلم : [ ما من قوم يقومون من مجلس ولا يذكرون الله تعالى فيه إلا قاموا عن مثل جيفة حمار وكان لهم حسرة ] رواه أبو داود بإسناد صحيح 

Abu Hurairah (May Allah be pleased with him)reported: Messenger of Allah (PBUH) said, "Those people who leave a gathering in which they have not remembered Allah, will conclude it as if it has foul odour similar to that of a rotten carcass of a donkey. And it will be a cause of grief to them.'' [Abu Dawud, Sahih]. 

Commentary: Messenger of Allah (PBUH) has warned us against refraining from the remembrance of Allah because most of the heart diseases are caused by this indifference, and because most of the sins are committed as a result of this indifference. 

 وعنه رضي الله عنه عن النبي صلى الله عليه و سلم قال : [ ما جلس قوم مجلسا لم يذكروا الله تعالى فيه ولم يصلوا على نبيهم فيه إلا كان عليهم ترة فإن شاء عذبهم وإن شاء غفر لهم ] رواه الترمذي وقال حديث حسن 

Abu Hurairah (May Allah be pleased with him)reported: The Prophet (PBUH) said, "Whenever a group of people sit in a gathering in which they do not remember Allah the Exalted, nor supplicate to elevate the rank of their Prophet, such a gathering will be a cause of grief to them. If Allah wills, He will punish them, and if He wills He will forgive them.'' 

[Tirmidhi, Hasan]. 

Commentary: Any meeting where Allah (SWT) is not glorified and praised and His blessings are not invoked to elevate the rank of His Prophet (PBUH), will cause grief and punishment to the participants in the Hereafter. 

 وعنه رضي الله عنه عن رسول الله صلى الله عليه و سلم قال : [ من قعد مقعدا لم يذكر الله تعالى فيه كانت عليه من الله ترة ومن اضطجع مضجعا لا يذكر الله تعالى فيه كانت عليه من الله ترة ] رواه أبو داود

Abu Hurairah (May Allah be pleased with him)reported: Messenger of Allah (PBUH) said, "If anyone sits in a gathering where he does not remember Allah, he will bring grief upon himself (on the Day of Resurrection), and he who lies down in a place where he does not remember Allah, will bring grief upon himself (on the Day of Resurrection).'' 

[Abu Dawud]. 

Commentary: To sum up what has gone in these Ahadith, man should remember Allah on all occasions. This will establish and cement his bond with Allah, keeping heedlessness away from his heart and mind. It is heedlessness which prompts man to transgress Divine rules and limits, whereas the remembrance of Allah prevents him from indulging in backbiting and passing slanderous remarks against people in their absence or reproaching and belittling someone at a meeting. Unfortunately, such petty and negative out-pourings are relished at chat sessions in our society. This generates grudge, ill-will and hostility in hearts and splits up social cohesion and Islamic solidarity. Every Muslim should, therefore, take care to avoid such gatherings. 

THE EXPIATION OF ASSEMBLY (Kaffaaratul Majlis)

Aishah (RA) said: "Allah's Messenger (SAW) did not sit in a gathering, and did not recite the Qur'an, and did not perform any prayer without concluding by saying :

سُبْحَانَكَ اللّٰهُـمَّ وَبِحَمْدِكَ، أَشْهَـدُ أَنْ لاَّ إِلٰهَ إِلاَّ أَنْتَ أَسْتَغْفِرُكَ وَأَتُوْبُ إِلَيْكَ.

Transliteration:

Subhaanaka Allaahumma wa bihamdika, ash-hadu an laa ilaaha illa Anta, astaghfiruka wa atoobu ilaika.

Translation:

Glory is to You. O Allah, and praise is to You. I bear witness that there is none worthy of worship but You. I seek Your forgiveness and repent to You.

[Abu Dawud, Ibn Majah, Tirmidhi and Nasa'i-Sahih]

Abu Dawood narrated that Abu Barzah al-Aslami (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) used to say, when he wanted to leave a gathering: “Glory and praise be to You, O Allah, there is no god but You, I seek Your forgiveness and I repent to You.” A man said: O Messenger of Allah, you are saying something that you did not say before. He said: “It is expiation for anything that happened in the gathering.”

Reciting Surah al-‘Asr before leaving a gathering:

This was the practice of the Sahabah (may Allah be pleased with them). 

It was narrated that Abu Madeenah al-Darimi said: When two men among the companions of the Prophet met, they did not part until one of them recited to the other Surah al-‘Asr, then one would say salam to (greet) the other.

(Abu Dawood (no. 417); al-Tabarani in al-Mu’jam al-Awsat (5/215); al-Bayhaqi in Shu’ab al-Eeman (6/501), Sahih)