How can one apply the effect of Aisha (may Allah be pleased with her), in which she mentioned that the Prophet (peace and blessings of Allah be upon him) used to conclude his gatherings, recitations, and prayers with certain words?

The expiation for a gathering (Kaffarat al-Majlis) is to say: "Subhanak Allahumma 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 repent to You) before leaving any gathering. It has been authentically reported from the Prophet (peace be upon him) that whoever says this, whatever shortcomings occurred in that gathering will be forgiven. Aisha (may Allah be pleased with her) explained that the Prophet (peace be upon him) used to conclude every gathering with this supplication, whether it was a gathering of remembrance (dhikr), Quran recitation, or prayer. If the gathering was for good, this supplication served as a seal that affirmed that good and elevated it to the level of acceptance. If it was otherwise, it served as an expiation for any shortcomings therein. It is recommended for a Muslim to conclude any gathering they attend with this remembrance, but it is not permissible to rely on it to be lenient with sins such as backbiting and slander, as such injustices require seeking forgiveness from those who were wronged.