Omnia munda mundis, literally meaning "to the pure [men], all things [are] pure", is a Latin sentence that has entered a relatively common usage in many countries. The phrase is from the Latin translation of the New Testament:

"Omnia munda mundis; coinquinatis autem et infidelibus nihil mundum, sed inquinatae sunt eorum et mens et conscientia"

("To the pure all things are pure; but to those who are defiled and unbelieving nothing is pure, but both their mind and their conscience are defiled") - Epistle of Paul to Titus, I:15