ما هو السند الشرعي لاعتزال أهل السنة والجماعة للمساجد وغيرها؟

The Sunni Muslims (Ahl al-Sunnah wa al-Jama'ah) believe that attending congregational prayers in mosques is a manifestation of the obligatory شعائر الإسلام (rituals/symbols of Islam) that must be displayed. It is forbidden for the people of a town to collude in abandoning congregational prayer, and this is counted among the major sins (al-kaba'ir). Scholars have differed on fighting the people of a town who agree to abandon it, with two opinions. These two opinions are two narrations within the Hanbali school of thought. The relied-upon opinion among them is that they are not to be fought if it is a Sunnah. However, according to the opinion that it is Fard Kifayah (a collective obligation), they are to be fought for abandoning it if they collectively agree not to establish it.

Lagging behind in congregational prayer is not in any way from the practice of Ahl al-Sunnah wa al-Jama'ah. Rather, whoever considers lagging behind in congregational prayer a religion is an innovator (mubtadi') and misguided.