Every year, millions of Muslim men from around the world gather by the banks of the Turag River in Tongi, Bangladesh, for a three-day celebration of Islam. The annual event, known as Bishwa Ijtema (Bengali for "world gathering), is organized and hosted by a group known as Tablighi Jama'at (Proselytizing Group). Although the group is little-known outside the Muslim community, it has one of the largest followings in the world. In 2008, it was...