Elbert Hubbard (1908). “Little Journeys to the Homes of Great Teachers ...: no. 1. Booker T. Washington. no. 2. Thomas Arnold. no. 3. Erasmus. no. 4. Hypatia. no. 5. St. Benedict. no. 6. Mary Baker Eddy”
Dr. Robert C. Worstell, Dorothea Brande, Claude M. Bristol, Earl Nightingale, Napoleon Hill (2017). “Mindset StackingTM Inspirational Journal VolumeSS01”, p.122, Lulu.com
"The New Dictionary of Thoughts: A Cyclopedia of Quotations from the Best Authors of the World, both Ancient and Modern". Book compiled by Tryon Edwards et al., 1960.