Neglected Sunan Concerning Majlis (assembly, gathering)

- Kaffaratul-Majlis (The Expiation of Assembly)
 
Subhaanaka Allaahumma wa bihamdika, ash-hadu anlaa-ilaaha-illaa-Anta, astaghfiruka wa atoobu 'ilayka (which means: Free from any imperfection are You, Oh Allaah, and all Praise is for You. I bear witness that there is none worthy of worship except You. I seek Your forgiveness and repent to You). [Abu Dawood, Ibn Maajah, At-Tirmithee and An-Nasa`ee; Al-Albaanee, Saheeh At-Tirmithi 3/ 153]  

'Aa`ishah (رضى الله عنها) said: "Allaah's Messenger (صلى الله عليه وسلم) did not sit in a gathering, and did not recite the Qur`aan, and did not perform any prayer without concluding by saying...(then she quoted the above)." This was reported by An-Nasaa`ee in 'Amalul-Yawm wal-Laylah (no.308). This hadeeth is authentic with and without the extra wording. For further detail about its chain of transmission, refer back to Al-Albaanee's Silsilahtus Saheeh (80). May Allaah have mercy upon him.
 
 
- What to say while sitting in an assembly
 
Ibn 'Umar (radiAllaahu 'anumma) said: "We used to count that Allaah's Messenger (صلى الله عليه وسلم) used to say one hundred times in a gathering: Rabb-ighfirlee wa toob 'alayya innaka Antat-Tawwaabul-Ghafoor(which means: My Lord, forgive me and accept my repentance, for You are the Acceptor of repentance, The All-Forgiving)."  
 
Also: Rabb-ighfirlee wa toob 'alayya innaka Antat-Tawwaabur-Raheem (which means: My Lord, forgive me and accept my repentance, for You are the Acceptor of repentance, The Specifically Merciful).
 
[Saheeh Ibn Maajah (2/321); Al-Albaanee, Saheeh At-Tirmithee 3/153]