Hadith: If people sit in a session where they neither remember Allah nor invoke blessings upon the Prophet (may Allah's peace and blessings be upon him) that will be for them a cause of grief on the Day of Judgment

عن أبي هريرة رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : «ما قعد قوم مقعداً لم يذكروا الله، ولم يصلوا على النبي صلى الله عليه وسلم إلا كان عليهم حسرة يوم القيامة».
[صحيح] - [رواه الترمذي]

Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "c2">“If people sit in a session where they neither remember Allah nor invoke blessings upon the Prophet (may Allah's peace and blessings be upon him) that will be for them a cause of grief on the Day of Judgment.”
Sahih/Authentic. - [At-Tirmidhi]

Explanation

This Hadīth indicates the regret and loss of those who sit in a gathering and leave it without making mention of Allah in their hearts or on their tongues. Likewise, they neither make mention of the Prophet, nor do they invoke Allah's blessings on him. These types of gatherings will be a cause of grief on the Day of Judgment, because people who were there did not benefit from them in the real sense. The situation is quite serious when forbidden things are committed, such backbiting, etc. So once in a gathering, one should remember Allah, the Almighty, and invoke Allah's peace and blessings upon the Prophet.