It is narrated from Abu Hurayrah and Jabir bin Abdullah (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 people until they affirm the word of tawhid. When they affirm it, they have protected their blood and their wealth from me, except by its right, and their reckoning is with Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15845