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 the Messenger of Allah said:

I have been commanded to fight against people so long as they do not declare that there is no god but Allah, and he who professed it was guaranteed the protection of his property and life on my behalf except for the right affairs rest with Allah.
وَحَدَّثَنَا أَبُو الطَّاهِرِ، وَحَرْمَلَةُ بْنُ يَحْيَى، وَأَحْمَدُ بْنُ عِيسَى، قَالَ أَحْمَدُ حَدَّثَنَا وَقَالَ الآخَرَانِ، أَخْبَرَنَا ابْنُ وَهْبٍ، قَالَ أَخْبَرَنِي يُونُسُ، عَنِ ابْنِ شِهَابٍ، قَالَ حَدَّثَنِي سَعِيدُ بْنُ الْمُسَيَّبِ، أَنَّ أَبَا هُرَيْرَةَ، أَخْبَرَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ أُمِرْتُ أَنْ أُقَاتِلَ النَّاسَ حَتَّى يَقُولُوا لاَ إِلَهَ إِلاَّ اللَّهُ فَمَنْ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ عَصَمَ مِنِّي مَالَهُ وَنَفْسَهُ إِلاَّ بِحَقِّهِ وَحِسَابُهُ عَلَى اللَّهِ ‏"‏ ‏.‏
Reference : Sahih Muslim 21 a
In-book reference : Book 1, Hadith 33
USC-MSA web (English) reference : Book 1, Hadith 30
  (deprecated numbering scheme)