Voltaire quotes

No. Evelyn Beatrice Hall wrote the sentence in 1906 in The Friends of Voltaire, summarizing his attitude in her own words, and later confirmed the phrasing was hers. Voltaire's documented views on tolerance are real; this sentence is not his.

“We must cultivate our garden” — the closing reply of Candide, the fictional hero of Voltaire's 1759 tale of the same name, setting patient, concrete work against the systems of his tutor Pangloss. It is the book's last word and Voltaire's most quoted line of fiction.

Yes — “Si Dieu n'existait pas, il faudrait l'inventer,” from his 1768 verse epistle answering an atheist tract. In its poem the line argues for belief's usefulness, not against belief.

In a 1770 letter to Frederick William, Prince of Prussia: “Doubt is not a pleasant condition, but certainty is an absurd one.”

“Crush the infamous thing” — Voltaire's battle-cry against religious persecution and fanaticism, used as the sign-off of his campaign letters through the 1760s and often abbreviated to “Écr. l'inf.”

That is a loose rendering of a real sentence: “Le sens commun est fort rare” — common sense is very rare — from the “Sens commun” entry of his Philosophical Dictionary (1764).