Prejudice, not being founded on reason, cannot be removed by argument.

Samuel Johnson (1709–1784) English writer, lexicographer, critic

(Spurious)
    (Source)

Frequently attributed without citation, and not found in Johnson's works.  However, the phrase can be found in other contexts:

• "This objection on the score of color is founded upon prejudice, and hence cannot be removed by argument, for prejudice is blind and listens not to reason." -- Rep. Godlove S. Orth of Indiana, speech before the House of Representatives (5 Apr 1869) on the question of admitting the Dominican Republic as a US territory.
• "This persuasion of the power of the priest is, as we have said, a traditional prejudice; it is not founded on any reasons or proofs addressed to the understanding, and therefore it cannot be removed by argument." -- John Eliot Howard, The Island of the Saints (1855), quoting from the Achill Herald (Jun 1855).