The Hadith, which is a set of additional Muslim texts written after the Koran, describe how the prophet Mohamed prepared to attack the Jews in Khaibar in 628 CE. As he begins the battle, he shouts “Allahu Akbar.”
The exact quote from the Hadith is: “The Prophet set out for Khaibar and reached it at night. He used not to attack if he reached the people at night, till the day broke. So, when the day dawned, the Jews came out with their bags and spades. When they saw the Prophet; they said, ‘Muhammad and his army!’ The Prophet said, ‘Allahu Akbar! (Allah is Greater) and Khaibar is ruined, for whenever we approach a nation [i.e. enemy to fight] then it will be a miserable morning for those who have been warned.’” “Allahu” is the nominative form of the word “Allah,” the name of God in Islam. It is not God. There is a significant difference between the name of God and the word “god.”