Christianity
La nôtre [religion] est sans contredit la plus ridicule, la plus absurde, et la plus sanguinaire qui ait jamais infecté le monde.
"[Christianity] is assuredly the most ridiculous, the most absurd and the most bloody religion which has ever infected this world. Your Majesty will do the human race an eternal service by extirpating this infamous superstition, I do not say among the rabble, who are not worthy of being enlightened and who are apt for every yoke; I say among honest people, among men who think, among those who wish to think. ... My one regret in dying is that I cannot aid you in this noble enterprise, the finest and most respectable which the human mind can point out.."
In La bible enfin expliquee, he considered Bible as:
It is characteristic of fanatics who read the holy scriptures to tell themselves: God killed, so I must kill; Abraham lied, Jacob deceived, Rachel stole: so I must steal, deceive, lie. But, wretch, you are neither Rachel, nor Jacob, nor Abraham, nor God; you are just a mad fool, and the popes who forbade the reading of the Bible were extremely wise.
Mohammed
In his tragedy Le Fanatisme ou Mahomet, Voltaire described Mohammed as an "impostor", a " false prophet", a "fanatic" and a "hypocrite". Voltaire defended the play, he said that he "tried to show in it into what horrible excesses fanaticism, led by an impostor, can plunge weak minds".