The Book of Etiquette in Islam.

Riyad as-Salihin, The Book of the Etiquette of Sleeping, Lying and Sitting etc
Book 5, Hadith 828
Narrated 'Salman Al-Farisi (ra):
Messenger of Allah (pbuh) said, "If a man takes a bath on Friday, purifies himself thoroughly, uses oil and perfume which is available in the house, sets forth for the mosque, does not (forcibly) sit between two persons, offers the prayer that is prescribed for him and listens to the Imam silently, his sins between this Friday and the previous Friday will be forgiven."[Al- Bukhari].

Riyad as-Salihin, The Book of the Etiquette of Sleeping, Lying and Sitting etc
Book 5, Hadith 829
Narrated 'Amr bin Shu'aib on the authority of his father and grandfather reported:
Messenger of Allah (pbuh) said, "It is not permissible for a person to sit between two people without their permission."[At-Tirmidhi].

Riyad as-Salihin, The Book of the Etiquette of Sleeping, Lying and Sitting etc
Book 5, Hadith 832
Narrated 'Abu Hurairah (ra):
Messenger of Allah (pbuh) said, "Whoever sits in a gathering and indulges in useless talk and before getting up supplicates: 'Subhanaka Allahumma wa bihamdika, ash-hadu an la ilaha illa Anta, astaghfiruka wa atubu ilaika (O Allah, You are free from every imperfection; praise be to You. I testify that there is no true god except You; I ask Your Pardon and turn to You in repentance),' he will be forgiven for (the sins he may have intentionally or unintentionally committed) in that assembly."[At-Tirmidhi].