When when Jibril (Gabriel) asked the Prophet (peace be upon him) about Islam and faith, he replied, Islam is that you testify that there is no one worthy of worship but Allah and that Muhammad is Allah's Messenger, establish prayer, pay Zakah (the obligatory charity), observe the fast of Ramadan, and perform Hajj (pilgrimage) to the House (Ka`bah) if you are able. Then, he (peace be upon him) defined faith, To believe in Allah, His Angels, His Books, His Messengers, the Last Day, and to believe in the Divine Predestination whether good or bad. He (peace be upon him) mentioned the principles of faith upon which Islam is based and the foundational pillars of Islam which it is established on.
The pillars of Islam are five: The two testimonies of faith, Salah, Zakah, Sawm, and Hajj. The inherent pillars of Islam are the six foundations of Iman on which Islam is built; to believe in Allah, His Angels, His Books, His Messengers, the Last Day, and Divine Decree whether good or bad. Neither Islam nor Iman can stand apart from each other; both are essential.