Is it obligatory to mention Allah in every gathering, based on the Prophet’s (PBUH) saying: "No people sit in a gathering in which they do not mention Allah nor invoke blessings upon their Prophet, except that it will be a source of regret for them. If He wills, He will punish them, and if He wills, He will forgive them," or does the Hadith indicate dislike (karahah)?

The aforementioned Hadith is authentic. The majority of scholars hold that the remembrance of Allah (dhikr) and sending blessings upon the Prophet (peace be upon him) is obligatory once in a lifetime, and anything beyond that is supererogatory (sunnah) and meritorious. Some virtuous individuals have compiled what is obligatory once in a lifetime, and it includes: the Basmalah (saying "Bismillah"), the Hamdalah (saying "Alhamdulillah"), the Tahlil (saying "La ilaha illa Allah"), seeking forgiveness (Istighfar), the Hawqalah (saying "La hawla wa la quwwata illa billah"), Tasbih (saying "Subhanallah"), Takbir (saying "Allahu Akbar"), seeking refuge (Ta'awwudh), sending blessings and peace upon the Prophet, and supplicating for parents and the righteous predecessors. What is mentioned in the Hadith falls under the category of emphasizing and intensifying, or on the premise of the occurrence of something that necessitates punishment from the people present in the gathering; for Allah does not punish except for committing a forbidden act or neglecting an obligation.