Mishkat al-Masabih 4
Ibn ‘Umar reported God's messenger as saying, “Islam is based on five things:
the testimony that there is no god but God and that Muhammad is His servant and messenger, the observance of the prayer, the payment of zakat , the Pilgrimage, and the fast during Ramadan.”

(Bukhari and Muslim.)
وَعَنِ ابْنِ عُمَرَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: 
" بُنِيَ الْإِسْلَامُ عَلَى خَمْسٍ: شَهَادَةِ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَأَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ وَإِقَامِ الصَّلَاةِ وَإِيتَاءِ الزَّكَاةِ وَالْحَجِّ وَصَوْمِ رَمَضَانَ "