William Shakespeare (1790). “The plays and poems of William Shakspeare, with the corrections and illustr. of various commentators; to which are added An essay on the chronological order of his plays; an essay relative to Shakspeare and Jonson; a dissertation on the three parts of King Henry vi; an historical account of the English stage; and notes. By E. Malone. 10 vols. [in 11 pt.].”, p.529
Letter to Duc de Richelieu, 18 June 1744. Although this saying is now associated with Voltaire, he is obviously quoting an Italian proverb here. The French form, which he used later, is Le mieux est l'ennemi du bien.
Sir Joshua Reynolds, Edward Malone (1867). “The Works of Sir Joshua Reynolds: Containing His Discourses, Idlers, A Journey to Flanders and Holland, and His Commentary on Du Fresnoy's Art of Painting; to which is Prefixed an Account of the Life and Writings of the Author by Edward Malone”, p.19