Is the loud, communal ذكر (dhikr - remembrance of God) an innovation (bid‘ah)? And to what extent is it valid to use the hadith: "What has made you sit?" They said: "We have sat to remember Allah and to praise Him for guiding us to Islam and for bestowing His grace upon us," as proof for its permissibility? Are there disagreements among scholars on this issue?

It is permissible to raise the voice in remembrance (dhikr) after prayers, provided it does not disturb those who are praying. However, general dhikr performed loudly and collectively is an innovation (bid'ah). Umar ibn al-Khattab (may Allah be pleased with him) disciplined people who gathered for supplication (du'a). The dislike for raising the voice in dhikr and du'a collectively intensifies if it causes harm to others. As for the hadiths that speak of people gathering to remember Allah or recite the Quran, there is no evidence in them that this was done collectively or in a loud voice; rather, it is probable that they were studying in turns or listening.