Abdullah bin Omar narrated that the messenger of Allah, sallallahu 'alayhi wasallam, said:

"I have been ordered to fight against people until they testify that there is no god but Allah and that Muhammad is the messenger of Allah and until they perform the prayers and pay the zakat, and if they do so they will have gained protection from me for their lives and property, unless [they do acts that are punishable] in accordance with Islam, and their reckoning will be with Allah the Almighty."

[Al-Bukhari and Muslim)