Question: Is it permissible for a Salafi to participate with the people of innovation in their masajid — for example, by delivering sermons or lectures there —

Answer: The scholars — may Allah’s mercy be upon them — have stated that masajid fall into three categories: First Category: Masajid of Ahlus-Sunnah — that is, masajid dedicated exclusively to the Sunnah and its people, with those who maintain them being from Ahlus-Sunnah, loving the Sunnah and supporting its adherents. There is no doubt that every Muslim, and in particular every Sunni, should support these masajid — whether through delivering sermons, lectures, or similar activities — so that the masajid of Ahlus-Sunnah may flourish. This is praiseworthy, and for this reason the Messenger of Allah ﷺ used to go to the masjid of Qubāʾ to revive it and pray two rakʿahs there. Allah, Exalted is He, commanded this when He said: “Never stand therein. Indeed, a masjid founded upon piety from the first day is more worthy for you to stand in…” The masajid of Ahlus-Sunnah are originally founded upon piety. This is their status. Second Category: Masajid of Ahlul-Ahwāʾ wal-Bidaʿ — masajid dedicated entirely to the people of innovation and maintained exclusively by them, known to the public as belonging to such groups, whether they are hizbi groups or Sufi orders. These masajid have two situations according to Ahlus-Sunnah wal-Jamāʿah: 1. If they are located in a town where there are also masajid of Ahlus-Sunnah, then it is not proper for a Sunni to go to the masajid of the people of innovation. This is a grave mistake. It constitutes cooperation with them and is not permissible. It spreads evil among the Muslims because people will say, “So-and-so, a person of knowledge, only went to them because he is one of them.” This promotes innovation. 2. If they are in a town where there are no masajid of Ahlus-Sunnah, then it is permissible to go to such masajid — but not for the purpose of reviving them; rather, to spread the Sunnah among their congregants. This is because the choice is either to remain at home and not call to Allah at all, or to give daʿwah in their masajid, thus committing the lesser of two evils — if they permit it. In that case, one may deliver lectures and sermons there. Evidence for this is found in the practice of the Messenger of Allah ﷺ, who used to go to the marketplaces and gatherings of Quraysh, calling them to Allah and saying, “Say: there is no deity but Allah, and you will be successful.” He did not confine himself to the masjid, but went out to them — especially in cases of necessity, when no one would come to him or know of him. In such cases, one must go to them and call people to the truth and to tawḥīd, as the Prophet ﷺ did. If they do not permit speaking from the front, one may sit at the back of the masjid. Third Category: Masajid of the general public. It is permissible to give lectures and sermons in these Masajid, but without public announcements. --- Answered by our esteemed Shaykh, Abū Mashkūr Al-Isrāfīlī—may Allah preserve and protect him. Source: https://t.me/Abumaskur/3386