Narrated Abu Huraira:Allah's Apostle said, " I have been ordered to fight with the people till they say, 'None has the right to be worshipped but Allah,' and whoever says, 'None has the right to be worshipped but Allah,' his life and property will be saved by me except for Islamic law, and his accounts will be with Allah, (either to punish him or to forgive him)

English translation · Sahih al-Bukhari