It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "I have been commanded to fight the people until they testify that there is no god but Allah and that Muhammad (peace and blessings be upon him) is the Messenger of Allah, and establish the prayer and pay the zakah. When they do that, they have protected their blood and their wealth from me, except by the right of Islam, and their reckoning is with Allah Almighty."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6501