“Knowledge, absolutely sure of its infallibility, is faith.”

Section 13; often the final portion of this is quoted alone as: "Absolute faith corrupts as absolutely as absolute power."
Reflections on the Human Condition (1973)
Context: The Savior who wants to turn men into angels is as much a hater of human nature as the totalitarian despot who wants to turn them into puppets.
There are similarities between absolute power and absolute faith: a demand for absolute obedience; a readiness to attempt the impossible; a bias for simple solutions — to cut the knot rather than unravel it; the viewing of compromise as surrender; the tendency to manipulate people and "experiment with blood."
Both absolute power and absolute faith are instruments of dehumanization. Hence absolute faith corrupts as absolutely as absolute power.

On the advisableness of improving natural knowledge (1866) http://www.gutenberg.org/dirs/etext01/thx1410.txt
1860s
Context: The improver of natural knowledge absolutely refuses to acknowledge authority, as such. For him, scepticism is the highest of duties; blind faith the one unpardonable sin. And it cannot be otherwise, for every great advance in natural knowledge has involved the absolute rejection of authority, the cherishing of the keenest scepticism, the annihilation of the spirit of blind faith; and the most ardent votary of science holds his firmest convictions, not because the men he most venerates hold them; not because their verity is testified by portents and wonders; but because his experience teaches him that whenever he chooses to bring these convictions into contact with their primary source, Nature — whenever he thinks fit to test them by appealing to experiment and to observation — Nature will confirm them. The man of science has learned to believe in justification, not by faith, but by verification.

The Virtue of Selfishness (1964)

Source: Absolution Gap (2003), Chapter 5 (p. 75)

Source: Angels & Demons

From Certainty to Uncertainty (2002)

In response to an article in the TIMES, London, which had labelled Islam as an "intolerant" religion, and held it responsible for some of the problems of the Middle East.
Context: Even a little knowledge of Islam will show that its religion is not only tolerant of other Faiths, but most respectful, and indeed, fully accepts the divine inspiration of all theistic Faiths that came before Islam. It does not only teach tolerance to its followers, but goes a step further and enjoins on them all to create the godly quality of "Hilm" that is, tolerance, forbearance, patience, calmness, and forgiveness. It is due to the spirit of tolerance of Islam that even the smallest Christian and Jewish minorities survived and kept all their doctrines during the thousand years of Muslim rule. Nothing like what happened to Muslims in Spain after the Christian conquest has ever happened to a non-Muslim Faith in any Islamic dominion. How, can Europeans be so ignorant as to have forgotten that in the first century of Islam the Khalifs ordered that all that was best in Greek and Roman cultures should be assimilated; that not only the philosophy, medicine and science of Greece, but its poetry and drama, were carefully translated into Arabic and were generally sought not only by the learned but also by the pious! The Muslim attitude towards the absorption of ideas was based on the principle of Islam which enjoins to acquire knowledge wherever available, and there is a well-known and authentic saying of the Prophet that "his followers should seek learning even if they have to go to China."

Source: Morals and Dogma of the Ancient and Accepted Scottish Rite of Freemasonry (1871), Ch. XXXII : Sublime Prince of the Royal Secret, p. 841
Context: All hypotheses scientifically probable are the last gleams of the twilight of knowledge, or its last shadows. Faith begins where Reason sinks exhausted. Beyond the human Reason is the Divine Reason, to our feebleness the great Absurdity, the Infinite Absurd, which confounds us and which we believe. For the Master, the Compass of Faith is above the Square of Reason; but both rest upon the Holy Scriptures and combine to form the Blazing Star of Truth.
All eyes do not see alike. Even the visible creation is not, for all who look upon it, of one form and one color. Our brain is a book printed within and without, and the two writings are, with all men, more or less confused.