Sahih Muslim Book 1 - Hadith 19-22

It is narrated on the authority of ('Abdullah) son of Umar (may Allah be pleased with them) that the Prophet (may peace of Allah be upon him) said:

(The superstructure of) al-Islam is raised on five (pillars), i. e. the oneness of Allah, the establishment of prayer, payment of Zakat, the, fast of Ramadan, Pilgrimage (to Mecca). A person said (to 'Abdullah b. Umar the narrator): Which of the two precedes the other-Pilgrimage or the fasts of Rarnadan? Upon this he (the narrator) replied: No (it is not the Pilgrimage first) but the fasts of Ramadan precede the Pilgrimage. (Sahih Muslim Book 1 - Hadith 19)

It is narrated on the authority of ('Abdullah) son of 'Umar, that the Prophet (may peace of Allah be upon him) said:

(The superstructure of) al-Islam is raised on five (pillars), i. e. Allah (alone) should be worshipped, and (all other gods) beside Him should be (categorically) denied. Establishment of prayer, the payment of Zakat, Pilgrimage to the House, and the fast of Ramadan (are the other obligatory acts besides the belief in the oneness of Allah and denial of all other gods). (Sahih Muslim Book 1 - Hadith 20)

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. (Sahih Muslim Book 1 - Hadith 21)

It is reported on the authority of Ta'us that a man said to 'Abdullah son of 'Umar (may Allah be pleased with him). Why don't you carry out a military expedition? Upon which he replied:

I heard the messenger of Allah (ﷺ) say: Verily, al-Islam is founded on five (pillars): testifying the fact that there is no god but Allah, establishment of prayer, payment of Zakat, fast of Ramadan and Pilgrimage to the House. (Sahih Muslim Book 1 - Hadith 22)