ALLAH'S MESSENGER (PBUH) SAID:
Islam is based on (the following) five (principles)
To testify that none has the right to be worshipped but ALLAH & Muhammad is ALLAH
To offer the (compulsory congregation ) prayer dutifully and perfectly.
To pay Zakat ( i.e obligatory charity ).
To perform Hajj. (i.e. Pilgrimage to Mecca )
To observe fast during the month of Ramadan.
SaHih Al-Bukhari 8