“It is a common sentence that knowledge is power; but who hath duly considered or set forth the power of ignorance? Knowledge slowly builds up what ignorance in an hour pulls down.”

Letter to W.T. Barry http://press-pubs.uchicago.edu/founders/documents/v1ch18s35.html (4 August 1822), in The Writings of James Madison (1910) edited by Gaillard Hunt, Vol. 9, p. 103; these words, using the older spelling "Governours", are inscribed to the left of the main entrance, Library of Congress James Madison Memorial Building.
1820s
Context: A popular Government without popular information, or the means of acquiring it, is but a Prologue to a Farce or a Tragedy, or perhaps both. Knowledge will forever govern ignorance: And a people who mean to be their own Governors, must arm themselves with the power which knowledge gives.

Rich Dad Poor Dad: What the Rich Teach Their Kids About Money-That the Poor and the Middle Class Do Not!

1 Corinthians 8:1
Source: Holy Hesychia: The Stillness that Knows God, p. 33

Source: In Praise of Philosophy (1963), p. 5
Context: Even those who have desired to work out a completely positive philosophy have been philosophers only to the extent that, at the same time, they have refused the right to install themselves in absolute knowledge. They taught not this knowledge, but its becoming in us, not the absolute but, at most, our absolute relation to it, as Kierkegaard said. What makes a philosopher is the movement which leads back without ceasing from knowledge to ignorance, from ignorance to knowledge, and a kind of rest in this movement.

Letter to W.T. Barry http://press-pubs.uchicago.edu/founders/documents/v1ch18s35.html (4 August 1822), in The Writings of James Madison (1910) edited by Gaillard Hunt, Vol. 9, p. 103; these words, using the older spelling "Governours", are inscribed to the left of the main entrance, Library of Congress James Madison Memorial Building.
1820s

Sometimes attributed to Hawking without a source, but originally from historian Daniel J. Boorstin. It appears in different forms in The Discoverers (1983), Cleopatra's Nose (1995), and introduction to The Decline and Fall of the Roman Empire (1995)
Misattributed