كتاب الإيمان
1
The Book of Faith
(5)
Chapter: Clarifying the pillars of Islam and its grand supports
(5)
باب بَيَانِ أَرْكَانِ الْإِسْلَامِ وَدَعَائِمِهِ الْعِظَامِ

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.
وَحَدَّثَنِي ابْنُ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا حَنْظَلَةُ، قَالَ سَمِعْتُ عِكْرِمَةَ بْنَ خَالِدٍ، يُحَدِّثُ طَاوُسًا أَنَّ رَجُلاً، قَالَ لِعَبْدِ اللَّهِ بْنِ عُمَرَ أَلاَ تَغْزُو فَقَالَ إِنِّي سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏ "‏ إِنَّ الإِسْلاَمَ بُنِيَ عَلَى خَمْسٍ شَهَادَةِ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَإِقَامِ الصَّلاَةِ وَإِيتَاءِ الزَّكَاةِ وَصِيَامِ رَمَضَانَ وَحَجِّ الْبَيْتِ ‏"‏ ‏.‏
Reference : Sahih Muslim 16 d
In-book reference : Book 1, Hadith 22
USC-MSA web (English) reference : Book 1, Hadith 21
  (deprecated numbering scheme)