there's no doubt that he changed arabia, and changed it from Paganism to monotheism, and made it a place of some morality (considering they had little morality at that time.) but nevertheless, even the people who knew Mohammad thought he was a madman.. look what the qu'ran says!!
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YUSUFALI: Therefore proclaim thou the praises (of thy Lord): for by the Grace of thy Lord, thou art no (vulgar) soothsayer, nor art thou one possessed.
PICKTHAL: Therefor warn (men, O Muhammad). By the grace of Allah thou art neither soothsayer nor madman.
SHAKIR: Therefore continue to remind, for by the grace of your Lord, you are not a soothsayer, or a madman.
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YUSUFALI: They say: "O thou to whom the Message is being revealed! truly thou art mad (or possessed)!
PICKTHAL: And they say: O thou unto whom the Reminder is revealed, lo! thou art indeed a madman!
SHAKIR: And they say: O you to whom the Reminder has been revealed! you are most surely insane:
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YUSUFALI: (And some said): "He is only a man possessed: wait (and have patience) with him for a time."
PICKTHAL: He is only a man in whom is a madness, so watch him for a while.
SHAKIR: He is only a madman, so bear with him for a time.
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YUSUFALI: Yet they turn away from him and say: "Tutored (by others), a man possessed!"
PICKTHAL: And they had turned away from him and said: One taught (by others), a madman?
SHAKIR: Yet they turned their backs on him and said: One taught (by others), a madman.
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YUSUFALI: But (Pharaoh) turned back with his Chiefs, and said, "A sorcerer, or one possessed!"
PICKTHAL: But he withdrew (confiding) in his might, and said: A wizard or a madman.
SHAKIR: But he turned away with his forces and said: A magician or a mad man.
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YUSUFALI: Similarly, no messenger came to the Peoples before them, but they said (of him) in like manner, "A sorcerer, or one possessed"!
PICKTHAL: Even so there came no messenger unto those before them but they said: A wizard or a madman!
SHAKIR: Thus there did not come to those before them a messenger but they said: A magician or a mad man.
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YUSUFALI: Therefore proclaim thou the praises (of thy Lord): for by the Grace of thy Lord, thou art no (vulgar) soothsayer, nor art thou one possessed.
PICKTHAL: Therefor warn (men, O Muhammad). By the grace of Allah thou art neither soothsayer nor madman.
SHAKIR: Therefore continue to remind, for by the grace of your Lord, you are not a soothsayer, or a madman.
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YUSUFALI: Before them the People of Noah rejected (their messenger): they rejected Our servant, and said, "Here is one possessed!", and he was driven out.
PICKTHAL: The folk of Noah denied before them, yea, they denied Our slave and said: A madman; and he was repulsed.
SHAKIR: Before them the people of Nuh rejected, so they rejected Our servant and called (him) mad, and he was driven away.
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YUSUFALI: Thou art not, by the Grace of thy Lord, mad or possessed.
PICKTHAL: Thou art not, for thy Lord's favour unto thee, a madman.
SHAKIR: By the grace of your Lord you are not mad.