What is the ruling on group takbir? Is it permissible or not?

It is true that the takbir (proclamation of 'Allahu Akbar') in specific situations, such as the days of Tashreeq and the first ten days of Dhu al-Hijjah, used to occur collectively. In Sahih al-Bukhari, it is narrated that Umar (may Allah be pleased with him) would proclaim the takbir in his tent in Mina, and the people would then proclaim the takbir after him until Mina reverberated with takbir. And it is narrated that Ibn Umar and Abu Hurayrah (may Allah be pleased with them both) used to go out to the marketplace during the ten days, proclaiming the takbir, and the people would then proclaim the takbir after them. This indicates the permissibility of collective takbir, not that performing it in congregation is the basis of its legislation or more complete than performing it individually.