Silsilat al-Ahadith al-Sahihah

Abdullah bin Umar (may Allah be pleased with them both) narrates 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 deity except Allah and that Muhammad (peace be upon him) is the Messenger of Allah. (After affirming this monotheism and messengership) they establish prayer and pay zakat. When they do this, they will have protected their blood and their wealth from me, except by the right of Islam. And their (inner) account is with Allah."