كتاب الإيمان
1
The Book of Faith
(8)
Chapter: The command to fight the people until they say "La ilaha illallah Muhammad Rasul-Allah", and establish Salat, and pay the Zakat, and believe in everything that the prophet (saws) brought. Whoever does that, his life and his wealth are protected except by its right, and his secrets are entrusted to Allah, the most high. Fighting those who withhold Zakat or other than that is one of the duties of Islam and the Iman should be concerned with the Laws of Islam
(8)
باب الأَمْرِ بِقِتَالِ النَّاسِ حَتَّى يَقُولُوا لاَ إِلَهَ إِلاَّ اللَّهُ مُحَمَّدٌ رَسُولُ اللَّهِ ‏‏

It is reported on the authority of Abu Huraira that he heard the Messenger of Allah say:

I have been commanded to fight against people, till they testify to the fact that there is no god but Allah, and believe in me (that) I am the messenger (from the Lord) and in all that I have brought. And when they do it, their blood and riches are guaranteed protection on my behalf except where it is justified by law, and their affairs rest with Allah.
حَدَّثَنَا أَحْمَدُ بْنُ عَبْدَةَ الضَّبِّيُّ، أَخْبَرَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي الدَّرَاوَرْدِيَّ - عَنِ الْعَلاَءِ، ح وَحَدَّثَنَا أُمَيَّةُ بْنُ بِسْطَامَ، - وَاللَّفْظُ لَهُ - حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، حَدَّثَنَا رَوْحٌ، عَنِ الْعَلاَءِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ يَعْقُوبَ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ أُمِرْتُ أَنْ أُقَاتِلَ النَّاسَ حَتَّى يَشْهَدُوا أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَيُؤْمِنُوا بِي وَبِمَا جِئْتُ بِهِ فَإِذَا فَعَلُوا ذَلِكَ عَصَمُوا مِنِّي دِمَاءَهُمْ وَأَمْوَالَهُمْ إِلاَّ بِحَقِّهَا وَحِسَابُهُمْ عَلَى اللَّهِ ‏"‏ ‏.‏
Reference : Sahih Muslim 21 b
In-book reference : Book 1, Hadith 34
USC-MSA web (English) reference : Book 1, Hadith 31
  (deprecated numbering scheme)