Islam is based on five (pillars

Hazrat Ibn Umar (May Allah be pleased with him) reported: The Messenger of Allah [SAWW](PBUH) said, "Islam is based on five (pillars): testifying that there is no true god except Allah and that Muhammad (PBUH) is His slave and Messenger; performing of Salat (Iqamat-as-Salat); the payment of Zakat; performing Hajj (pilgrimage) to the House [of Allah (Ka`bah)]; and Saum (fasting) during the month of Ramadan.'' 

[Al-Bukhari Book 01, Chapter 02, Hadith # 07] 

Lesson : as mentioned above in Surah Al-Hajj Ayat 25."the Path of Allah, and from Al-Masjid-al-Harâm (at Makkah) which We have made (open) to (all) men," In this Hadith, Islam has been compared to a building which rests on five pillars. As a building cannot stand without its foundation, similarly, Islam cannot exist without these pillars. For this reason, he who denies any one of these obligations is a disbeliever, and he who neglects any of them due to slackness or want of attention is a sinful and impious Muslim.