Muslim brothers and sisters in Islam certainly need to know these 4 kholaphadera biography.

Islam 4 kholapha
Abu Bakr (ra)
Umar Farooq (ra)
Uthman (ra) and
Hazrat Ali (R)
The life of this Application.

Source of the Cave and the short story of the Prophet Islamic encyclopedia (Islamic Foundation, Bangladesh).

Hopefully this Application ditch all Muslim brothers and sisters, of course, is not good.