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.”
[Al-Bukhari & Muslim]