Narrated Abu Huraira: When the Prophet died and Abu Bakr became his successor and some of the Arabs reverted to disbelief, `Umar said, O Abu Bakr! How can you fight these people although Allah's Apostle said, 'I have been ordered to fight the people till they say: 'None has the right to be worshipped but Allah, 'and whoever said, 'None has the right to be worshipped but Allah', Allah will save his property and his life from me, unless (he does something for which he receives legal punishment) justly, and his account will be with Allah?'