Since the fathers have often erred, as you yourself confess, who will make us certain as to wherein they have not erred, assuming their reputation is sufficient and should not be weighed and judged according to the divine Scriptures? … What if they erred in their interpretation, as well as in their life and writings? In that way you make gods of all that is human in us, and of men themselves; and the word of men you make equal to the Word of God. … The saints could err in their writings and sin in their lives, but the Scriptures cannot err.
Luther’s Works, 36:136.