Pope Innocent III (1198), Sermon IV: “The Roman Pontiff has no superior but God. Who, therefore (should a pope ‘lose his savor’) could cast him out or trample him under foot - since of the pope it is said ‘gather thy flock into thy fold’? Truly, he should not flatter himself about his power, nor should he rashly glory in his honor and high estate, because the less he is judged by man, the more he is judged by God.
Still the less can the Roman Pontiff glory [Minus dico] because he can be judged by men, or rather, can be shown to be already judged, if for example he should wither away into heresy; because he who does not believe is already judged.
In such a case it should be said of him: ‘If salt should lose its savor, it is good for nothing but to be cast out and trampled under foot by men’.”
(Sermo 4: In Consecratione PL 218:670.)