It was narrated from Ibn 'Umar that:

A man said to him: "Why don't you go out and fight?" He said: "I heard the Messenger of Allah ﷺ say: 'Islam is built on five (pillars): Testimony that there is none worthy of worship except Allah, establishing Salah, giving Zakah, Hajj, and fasting Ramadan.'"

أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ عَمَّارٍ، قَالَ حَدَّثَنَا الْمُعَافَى، - يَعْنِي ابْنَ عِمْرَانَ - عَنْ حَنْظَلَةَ بْنِ أَبِي سُفْيَانَ، عَنْ عِكْرِمَةَ بْنِ خَالِدٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَجُلاً، قَالَ لَهُ أَلاَ تَغْزُو قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ " بُنِيَ الإِسْلاَمُ عَلَى خَمْسٍ شَهَادَةِ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَإِقَامِ الصَّلاَةِ وَإِيتَاءِ الزَّكَاةِ وَالْحَجِّ وَصِيَامِ رَمَضَانَ " .