Romans 14:5

One person regards a certain day above the others, while someone else considers every day alike. Each one should be fully convinced in his own mind.

Titus 1:15

To the pure, all things are pure; but to the defiled and unbelieving, nothing is pure. Indeed, both their minds and their consciences are defiled

Proverbs 30:12

There is a generation of those who are pure in their own eyes and yet unwashed of their filth.