The thing he proposes to buy, is what cannot be sold—LIBERTY! For it, he has nothing to give: every thing of value which you possess, you obtained under a free constitution; part with it, and you must be not only a slave but an idiot.
Source, in full
Speech in the Irish House of Commons against the union with Great Britain (15 January 1800), quoted in The Speeches of The Right Honourable Henry Grattan, in the Irish, and in the Imperial Parliament, Vol. III (1822), pp. 372-373