A quote from the Charmides by Plato
"The question at issue is not who said it, but whether what he said is true or not." A good piece of advice that Socrates, in a discussion on what it means to be 'temperate', says to the young man Charmides. This principle is a precursor to the early churches saying, "All truth is God's Truth." The question is not where we find it, or who said it, but whether or not it is true.