Book Belief of Sahi Bukhari Narrated Ibn `Umar(R.A)

Narrated Ibn `Umar: Allah's Apostle said: Islam is based on
(the following) five (principles): −1. To testify that there
is no deity (owing the right to be worshipped) but Allah and
that Muhammad is Allah's Messenger. −2. To offer the
(compulsory congregational) prayers dutifully and perfectly.
−3. To pay Zakat (i.e. obligatory charity) . −4. To perform
Hajj. (i.e. Pilgrimage to Mecca) −5. To observe fast during
the month of Ramadan.
Sahi Bukhari: 1.7