When Qur'an becomes optional.
And when people with Muslim names start debating whether or not they should learn the Qur'an and how much of it they should learn.
When Arabic becomes a choice. When Arabic Language becomes one of many languages on a menu of options for Muslims to choose from.
And when people with Muslim names and backgrounds start arguing whether or not they should learn the Arabic Language and how much of it they should learn.
And when Learning Arabic Language and Learning the Qur'an figures way down in a long list of priorities in the lives of people with Muslim names and credentials.
When these things happen, it may be time to look out the window to see if Doomsday is around and if Qiyamat is approaching.