It is narrated from Sayyiduna Jubayr bin Mut'im (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever says these words: 'Subhanallahi wa bi hamdih, subhanaka Allahumma wa bi hamdik, ashhadu an la ilaha illa ant, astaghfiruka wa atubu ilayk' (Glory be to Allah and praise be to Him; glory be to You, O Allah, and praise; I bear witness that there is no god but You; I seek Your forgiveness and I repent to You); if he says them in a gathering of remembrance, they will be like a seal (a safeguard) upon the good of that gathering, and if he says them in a gathering of idle and useless talk, they will be an expiation for his sins." This hadith is sahih (authentic) on the condition of Imam Muslim, but the two Shaykhs did not record it.