Sayyiduna Abdullah bin Amr (may Allah be pleased with him) transmits this statement of the Prophet (peace and blessings be upon him): "The expiation for a gathering is:
'Subhanaka Allahumma wa bihamdika, ashhadu an la ilaha illa anta, astaghfiruka wa atubu ilayk' (Glory be to You, O Allah, and praise is Yours; I bear witness that there is no god but You; I seek Your forgiveness and turn to You in repentance)."
Tabarani recorded it; its chain contains a narrator, Muhammad bin Jami' al-Attar, whom Ibn Hibban declared thiqah (trustworthy) and a group declared da'if (weak); the rest of its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 17166