Hadith 3 - Islam is built upon five pillars

On the authority of Abu 'Abd al-Rahman 'Abdullah bin 'Umar bin al-Khattab, radiyallahu 'anhuma, who said: I heard the Messenger of Allah, sallallahu 'alayhi wasallam, say:"Islam has been built upon five things - on testifying that there is no god save Allah, and that Muhammad is His Messenger; on performing salah; on giving the zakah; on Hajj to the House; and on fasting during Ramadhan."

Bukhari & Muslim