What is the fatwa about gathering and having sermon inside a mosque immediatley after Jumah prayers?
Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
If the purpose of gathering after the prayer of Jumah or any other prayer is a religious one such as to gain Islamic knowledge, or to teach Islam to others, etc. then it is permitted, since the mosques are built for this purpose.
Leaving the mosque after completing the Friday prayer is not mandatory. Imam Ibn Atiyyah said explaining this verse: "Then when the (Jumu'ah) Salât (prayer) is finished, you may disperse through the land, …"[62:10] all the entire Muslim Ummah is in agreement that this rule is not mandatory rather it is only for permissibility. Imam Tabari narrated from Imam Zahhak that he said: 'the rule of dispersal in the above verse is only a permission of Allah. Therefore, one may sit there or may leave the mosque after Jumah prayer'.
However, if the gathering is not for a religious purpose then it is better to protect mosques from such matters.
Allah knows best.
You can search for fatwa through many choices