Sayyiduna Anas (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "The expiation for a gathering is that a person recites:
'Subhanaka Allahumma wa bihamdika, astaghfiruka wa atubu ilayk' (Glory be to You, O Allah, and praise is Yours; I seek Your forgiveness and turn to You in repentance)."
Al-Bazzar recorded it, and Tabarani in al-Awsat; its chain contains a narrator, Uthman bin Matar, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 17160