Q 15: What is the proof that Islam is defined as being the five pillars of this religion when considered in detail?
A--- The Prophet's saying (Peace be upon him) upon answering Gabriel when he asked about religion (Islam): "
"Al-Islam implies that you testify that there is no god but Allah and that Muhammad is the Messenger of Allah, and you establish prayer, pay Zakah, observe the fast of Ramadan, and perform pilgrimage to the House (the Ka' bah in Mecca), if one has the means to do so". (Bukhari and Muslim)
His saying (Peace be upon him) that reads:
"(The superstructure of) Islam is raised on five (pillars): The Oneness of Allah, performance of Prayer, payment of Zakah, fast of Ramadan, and Pilgrimage (to Mecca)".
(Bukhari and Muslim)
Reference: 200 FAQ On Muslims Belief - Shiekh Hafiz Ibn Ahmed Al Hakami