Then [the Banu Qurayza tribe] surrendered, and the apostle [Muhammad] confined them in Medina in the quarter of d. al-Harith, a woman of B. al-Najjar. Then the apostle went out to the market of Medina (which is still its market today) and dug trenches in it. Then he sent for them and struck off their heads in those trenches as they were brought out to him in batches. Among them was the enemy of Allah Huyayy b. Akhtab and Ka`b b. Asad their chief. There were 600 or 700 in all, though some put the figure as high as 800 or 900. As they were being taken out in batches to the apostle they asked Ka`b what he thought would be done with them. He replied, 'Will you never understand? Don't you see that the summoner never stops and those who are taken away do not return? By Allah it is death!' This went on until the apostle made an end of them.
Muhammad presides over the beheading of 600 to 900 Jews
From page 464 (690 in the Arabic) of the earliest Muslim biography of Muhammad:
