The people of the Book (dhimmi)-- those possessing scripture-- the Christians and the Jews, are placed under the protection of Islam and forbearance towards them was ordained by Muhammad: "Whoever kills one of the dhimmi will not inhale the fragrance of Paradise." Even the mere act of discriminating against the non-Muslims living under Islamic protection was considered a sinful transgression and the cause of crisis in affairs of empire: "When the dhimmi are oppressed, power goes into the hands of the enemy", "Whoever opprresses one of the dhimmi and lays upon him burdens that are too heavy, to him will I myself appear as an accuser on the Day of Judgment", "Whoever does any wrong to a Jew or a Christian will have me as accuser.": thus reads the oral traditional teaching of the Prophet. The Christian community of Nadjran was under Muhammad's protection: "If anyone encroaches upon their rights, I myself shall be his enemy and shall accuse him before God's countenance." Islam was not interested in making proselytes. The saying of the old Arab writer Ibn Sa'd is characteristic of the magnanimity of Islam: "If they become converted to Islam this is good; if they do not, let them remain (in their former faith); Islam is indeed spacious." (See Iw-War & Islam) (151:1)
Muhammad had allowed religious war when his community was being threatened by extermination: "And fight for the cause of God against those who fight against you: but commit not the injustice of attacking them first: God loveth not such injustice: And kill them wherever ye shall find them, and eject them from whatever place they have ejected you; for civil discord is worse than carnage... But if they desist, then verily God is Gracious, Merciful. Fight therefore against them until there be no more civil discord, and the only worship be that of God: but if they desist, then let there be no hostility."