Majjhima Nikaya 95

This I heard the Buddha said.
Religions, ideas, even people, may have a lot of faith and belief placed in them, but be hollow and empty and false - and others might have no faith or belief placed in them, and still be factual and true.

To say that what we believe and put faith in is true, and what we do not is false, is wrong.  To say that what we believe and put faith in is true means what is contrary to our beliefs and faith is false is wrong.  Even if many people agree with us, and hold similar beliefs, and faith. Even if these beliefs and faith have been maintained a very long time, and are traditional.

We may say "I know," and not know, "I see," and not see, and get others to do likewise - to their harm and suffering.

Truth may be elusive, but confidence is arrived at and discovered by making and then contemplating upon logical tests.  Fact may be elusive, but reasonable confidence is arrived at and discovered by repeating these tests.  It is by logic and reason we see when blind, we know despite ignorance.

Therefore, develop your capacity for testing, and contemplation.  Develop the desire to become willing to exert yourself.  Develop your curiosity if you would cultivate this desire for Dharma.

Majjhima Nikaya 95