If greatness of purpose, smallness of means, and astounding results are the three criteria of human genius, who could dare to compare any great man in modem history with Muhammad? The most famous men created arms, laws andempires only They founded, if anything at all, no more than material powers which often crumbled away before their eyes This man moved not only armies,legislation, empires, peoples and dynasties, but millions of men in one-third of the then-inhabited world; and more than that he moved the altars, the gods, the religions, the ideas, the beliefs and souls.... Hisforbearance in victory, his ambition which was entirely devoted to one idea and in no manner striving for an empire, his endless prayers, his 
mystic conversations with God, his death and his triumph after death-all these attest not to an imposture but to a firm conviction which gave him the power to restore a dogma. This dogma was twofold: the unity of God and theimmateriality of God; the former telling what God is, the latter telling what God is not; the one overthrowing false gods with the sword, the other starting an idea with the words. Philosopher, orator, apostle, legislator,warrior, conqueror of ideas, restorer of rational dogmas, of a cult without images; the founder of twenty terrestrial empires and of one spiritualempire, that is Muhammad. As regards all standards by which human greatness may be measured, we may well ask, is there any man greater than he? 
- Lamartine Histoire de la Turquie, Pans 1854, Vol. 11, pp. 276-77. 

It is not the propagation but the permanency of his religion that deserves our wonder; the same pure and perfect impression which he engraved at Mecca and Madina is preserved, after the revolutions of twelve centuries by the Indian, the African and the Turkish proselytes of the Koran... The Mahometans have uniformly withstood the temptation of reducing the object of their faith and devotion to a level with the senses and imagination of man.
I believe in One God and Mahomet is the Apostle of God' is the simple and invariable profession of Islam. The intellectual image of the Deity has never been degraded by any visible idol; the honors of the prophet have never transgressed the measure of human virtue; and his living precepts 
have restrained the gratitude of his disciples within the bounds of reason 
and religion. 

- Edward Gibbon and Simon Ocklay History of the Saracen Empire, London 1870, p 54. 

He was Caesar and Pope in one; but he was Pope without Pope's pretensions, Caesar without the legions of Caesar: without a standing army, without a bodyguard, without a palace, without a fixed revenue. If ever any man had the right to say that he ruled by the right divine, it was Mohammad, for he had all the power without its instruments and without its supports.
 
- Bosworth Smith Mohammad and Mohammadanism, London 1874, p 92. 

It is impossible for anyone who studies the life and character of the great Prophet of Arabia, who knows how he taught and how he lived, to feel anything but reverence for that mighty Prophet, one of the great messengers of the Supreme. And although in what I put to you I shall say many things which may be familiar to many, yet I myself feel whenever I re-read them, a new way of admiration, a new sense of reverence for that mighty Arabian teacher. 
- Annie Besant The Life and Teachings of Muhammad, Madras 1932, p 4 

His readiness to undergo persecution for his beliefs, the high moral character of the men who believed in him and looked up to him as leader, and the greatness of his ultimate achievement all argue his fundamental integrity To suppose Muhammad an impostor raises more problems than it solves. Moreover, none of the great figures of history is so poorlyappreciated in the West as Muhammad. 

- W Montgomery Watt Mohammad At Mecca, Oxford, 1953, p 52.