(5) باب بَيَانِ أَرْكَانِ الْإِسْلَامِ وَدَعَائِمِهِ الْعِظَامِ
It is narrated on the authority of 'Abdullah son of 'Umar that the Messenger of Allah (ﷺ) said:
(The superstructure of) al-Islam is raised on five (pillars), testifying (the fact) that there is no god but Allah, that Muhammad is His bondsman and messenger, and the establishment of prayer, payment of Zakat, Pilgrimage to the House (Ka'ba) and the fast of Ramadan.
Reference: Sahih Muslim 16 c
In-book reference: Book 1, Hadith 21
USC-MSA web (English) reference(deprecated numbering scheme): Book 1, Hadith 20