What is the recommended (masnun) to say before and after a good gathering?

Gathering with people is only commendable for good purposes, such as enjoining charity, a good deed, or reconciliation between people. It is preferable for such gatherings to take place in places of worship, and the assembly should not be devoid of the remembrance of Allah. It is sunnah to conclude the gathering with the supplication for expiation of the مجلس (assembly): "Subhanakallahumma wa bihamdika, ashhadu an la ilaha illa anta, astaghfiruka wa atubu ilayk." (Glory be to You, O Allah, and with Your praise, I bear witness that there is no god but You, I seek Your forgiveness and I repent to You.)