“There are few signs in a soul's state more alarming than that of religious indifference, that is, the spirit of thinking all religions equally true— the real meaning of which is, that all religions are equally false.”

Freedom of expression - Secular Theocracy Versus Liberal Democracy (1998)
Context: The Emergency which Islam had imposed after its advent in India and which had caused resentment among Hindus for a long time, now stood fully sanctioned by the Hindu elite. All religions were equal. But Islam was more equal.

Volume 1, Chapter 2 "Of the Union and Internal Prosperity of the Roman Empire, in the Age of the Antonines" http://www.ccel.org/ccel/gibbon/decline/files/volume1/chap2.htm. The portion regarding the views of the religions of the time taken by various constituencies has been misreported as Gibbon's own assessment of religion generally. See Paul F. Boller, John George, They Never Said It: A Book of Fake Quotes, Misquotes, and Misleading Attributions (1990), pp. 34–35.
The bold text has been misattributed to Lucretius and Seneca the Younger.
The Decline And Fall Of The Roman Empire (1776)
Source: The Decline and Fall of the Roman Empire
Context: The various modes of worship, which prevailed in the Roman world, were all considered by the people, as equally true; by the philosopher, as equally false; and by the magistrate, as equally useful. And thus toleration produced not only mutual indulgence, but even religious concord.
Context: The policy of the emperors and the senate, as far as it concerned religion, was happily seconded by the reflections of the enlightened, and by the habits of the superstitious, part of their subjects. The various modes of worship, which prevailed in the Roman world, were all considered by the people, as equally true; by the philosopher, as equally false; and by the magistrate, as equally useful. And thus toleration produced not only mutual indulgence, but even religious concord.
The superstition of the people was not embittered by any mixture of theological rancour; nor was it confined by the chains of any speculative system. The devout polytheist, though fondly attached to his national rites, admitted with implicit faith the different religions of the earth. Fear, gratitude, and curiosity, a dream or an omen, a singular disorder, or a distant journey, perpetually disposed him to multiply the articles of his belief, and to enlarge the list of his protectors. The thin texture of the Pagan mythology was interwoven with various but not discordant materials.

New York Times interview (2010) http://www.nytimes.com/2010/09/15/movies/15woody.html?_r=1&ref=arts#.

Source: The Gospel of Sri Ramakrishna (1942), p. 158
Context: One should not think, "My religion alone is the right path and other religions are false." God can be realized by means of all paths. It is enough to have sincere yearning for God. Infinite are the paths and infinite the opinions.

Speech, Marion, Ohio (31 July 1875)

Indian Spirituality and Life (1919)
Context: To the Indian mind the least important part of religion is its dogma; the religious spirit matters, not the theological credo. On the contrary to the Western mind a fixed intellectual belief is the most important part of a cult; it is its core of meaning, it is the thing that distinguishes it from others. For it is its formulated beliefs that make it either a true or a false religion, according as it agrees or does not agree with the credo of its critic. This notion, however foolish and shallow, is a necessary consequence of the Western idea which falsely supposes that intellectual truth is the highest verity and, even, that there is no other. The Indian religious thinker knows that all the highest eternal verities are truths of the spirit. The supreme truths are neither the rigid conclusions of logical reasoning nor the affirmations of credal statement, but fruits of the soul's inner experience. Intellectual truth is only one of the doors to the outer precincts of the temple. And since intellectual truth turned towards the Infinite must be in its very nature many-sided and not narrowly one, the most varying intellectual beliefs can be equally true because they mirror different facets of the Infinite. However separated by intellectual distance, they still form so many side-entrances which admit the mind to some faint ray from a supreme Light. There are no true and false religions, but rather all religions are true in their own way and degree. Each is one of the thousand paths to the One Eternal.

Ch 1 : "The Dickens Period"
Charles Dickens (1906)

R. Tagore, `Aatmaparichapa' in his book `Parichaya' http://hindusamhati.blogspot.com/2013/05/thoughts-of-rabindranath-tagore-on.html

As quoted in What Great Men Think of Religion (1972 [1945]) by Ira D. Cardiff, p. 245. Actually said by Edward Gibbonː "The various modes of worship, which prevailed in the Roman world, were all considered by the people, as equally true; by the philosopher, as equally false; and by the magistrate, as equally useful." (The History of the Decline and Fall of the Roman Empire, 1776, Vol. I, Ch. II).
Misattributed