Luther

And thus the Christian Church has held her own from the beginning until now among innumerable false spirits which have been from the beginning and may still come. And yet she goes on standing firmly by her Baptism, the Lord’s Supper, Gospel, Christ, and Ten Commandments, and true and pure prayer, and thus she judges and separates herself from all false teaching which is opposed to her—yes, even though the devil should become an angel of light and as a beautiful and radiant figure should present himself as God.—Exposition of Jn xiv, xv