“Today as always, men fall into two groups: slaves and free men. Whoever does not have two-thirds of his day for himself, is a slave, whatever he may be: a statesman, a businessman, an official, or a scholar.”

Source: The Liberty of Man, Woman and Child (1877)
Context: Only a few years ago there was a great awakening of the human mind. Men began to inquire by what right a crowned robber made them work for him? The man who asked this question was called a traitor. Others asked by what right does a robed hypocrite rule my thought? Such men were called infidels. The priest said, and the king said, where is this spirit of investigation to stop? They said then and they say now, that it is dangerous for man to be free. I deny it. Out on the intellectual sea there is room enough for every sail. In the intellectual air there is space enough for every wing.
The man who does not do his own thinking is a slave, and is a traitor to himself and to his fellow-men.

from his speech in Mallow, County Cork

As quoted by Stobaeus, iii.1.18

Majlisi, Bihārul Anwār, vol.78, p. 335.
Religious Wisdom

A Hero of Our Time (1840; rev. 1841)

In Search of the Miraculous (1949)

Harijan (24 February 1946). As quoted in The Politics Of Nonviolent Action, Gene Sharp, Porter Sargent Publishers (1973), p. 59
1940s

As quoted in "The Present Aspect of the Slavery Question" https://books.google.com/books?id=y3RaAAAAMAAJ&pg=PA69&dq=%22We+intend+this+Constitution+to+be+the+great+charter+of+human+liberty+to+the+unborn+%22&hl=en&sa=X&ved=0CB0Q6AEwAGoVChMI2ai6jcCsxwIVRRs-Ch38_wz2#v=onepage&q=%22We%20intend%20this%20Constitution%20to%20be%20the%20great%20charter%20of%20human%20liberty%20to%20the%20unborn%20%22&f=false (18 October 1859), by George William Curtis, Orations and Addresses of George William Curtis.

Source: The Underground History of American Education: An Intimate Investigation Into the Prison of Modern Schooling (2001), p. 62