Pope Leo XIII:
“But the supreme teacher in the Church is the Roman Pontiff. Union of minds, therefore, requires, together with a perfect accord in the one faith, complete submission and obedience of will to the Church and to the Roman Pontiff, as to God Himself. This obedience should, however, be perfect…(and) must consequently be accepted without wavering….
“Wherefore it belongs to the Pope to judge authoritatively what things the sacred oracles contain, as well as what doctrines are in harmony, and what in disagreement, with them; and also, for the same reason, to show forth what things are to be accepted as right, and what to be rejected as worthless; what it is necessary to do and what to avoid doing, in order to attain eternal salvation.”
(Source: Pope Leo XIII, inSapientiae Christianae (On Christians As Citizens), Encyclical promulgated on January 10, 1890, #22-24.)