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 has been narrated on the authority of Abdullah b. 'Umar that the Messenger of Allah said:

I have been commanded to fight against people till they testify that there is no god but Allah, that Muhammad is the messenger of Allah, and they establish prayer, and pay Zakat and if they do it, their blood and property are guaranteed protection on my behalf except when justified by law, and their affairs rest with Allah.
حَدَّثَنَا أَبُو غَسَّانَ الْمِسْمَعِيُّ، مَالِكُ بْنُ عَبْدِ الْوَاحِدِ حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ الصَّبَّاحِ، عَنْ شُعْبَةَ، عَنْ وَاقِدِ بْنِ مُحَمَّدِ بْنِ زَيْدِ بْنِ عَبْدِ اللَّهِ بْنِ عُمَرَ، عَنْ أَبِيهِ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ أُمِرْتُ أَنْ أُقَاتِلَ النَّاسَ حَتَّى يَشْهَدُوا أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ وَيُقِيمُوا الصَّلاَةَ وَيُؤْتُوا الزَّكَاةَ فَإِذَا فَعَلُوا عَصَمُوا مِنِّي دِمَاءَهُمْ وَأَمْوَالَهُمْ إِلاَّ بِحَقِّهَا وَحِسَابُهُمْ عَلَى اللَّهِ ‏"‏ ‏.‏
Reference : Sahih Muslim 22
In-book reference : Book 1, Hadith 36
USC-MSA web (English) reference : Book 1, Hadith 33
  (deprecated numbering scheme)