It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "I have been commanded to fight people until they affirm 'La ilaha illallah' (There is no god but Allah), establish the prayer and begin paying zakah. When they do this, their blood and their wealth become forbidden to me, but their matter rests with Allah Almighty."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13119