An Integral Spirituality
Context: Attunement could occur through any of the great religions, but would be tied exclusively to none of them. A person could be attuned to an "integral spirituality" while still be a practicing Christian, Buddhist, New-Age advocate, or Neopagan. This would be something added to one's religion, not subtracted from it. The only thing it would subtract (and there's no way around this) is the belief that one's own path is the only true path to salvation.
“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.”
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.
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Sri Aurobindo 224
Indian nationalist, freedom fighter, philosopher, yogi, gur… 1872–1950Related quotes

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

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.

"Q&A on The Parliament of the World's Religions," weekly mailing, 2007-SEP-05, as reported on Religious Tolerance.org http://www.religioustolerance.org/reltrue.htm

“Religions are not true or false, but better or worse.”
This statement is presented in quotes in The Philosophy of Religion and Advaita Vedanta (2008) by Arvind Sharma, p. 216, as a "Santayanan point", but earlier publications by the same author, such as in A Primal Perspective on the Philosophy of Religion (2006), p. 161, state it to be a stance of Santayana without actually indicating or in any ways implying that it is a direct quotation.
Disputed

Source: The Gospel of Sri Ramakrishna (1942), p. 158

“One religion is as true as another.”
Section 4, member 2, subsection 1, Religious Melancholy in defect; parties affected, Epicures, Atheists, Hypocrites, worldly secure, Carnalists; all impious persons, impenitent sinners, etc.
The Anatomy of Melancholy (1621), Part III

“Here, all ye learned, full of all Dispute,
Of true and false Religion lies the Root.”
"On Works of Mercy and Compassion, Considered as The Proofs of True Religion", St. 6
Miscellaneous Poems (1773)
Context: Here, all ye learned, full of all Dispute,
Of true and false Religion lies the Root.
The Mind of Christ, when He became a Man,
With all Its Tempers, forms its real Plan,
The Sheep from Goats distinguishing full well; —
His Love is Heav'n, and Want of It is Hell.