Papal Coronation Oath
To be taken by all Pontiffs of the Catholic Church, showing that no pontiff can not contradict the Deposit of Faith, or change/innovate in what has been handed down to him :
"I vow to change nothing of the received Tradition, and nothing thereof I have found before me guarded by my God-pleasing predecessors, to encroach upon, to alter, or to permit any innovation therein;
To the contrary: with glowing affection as her truly faithful student and successor, to safeguard reverently the passed-on good, with my whole strength and utmost effort;
To cleanse all that is in contradiction to the canonical order, should such appear; to guard the Holy Canons and Decrees of our Popes as if they were the divine ordinance of Heaven, because I am conscious of Thee, whose place I take through the Grace of God, whose Vicarship I possess with Thy support, being subject to severest accounting before Thy Divine Tribunal over all that I shall confess;
I swear to God Almighty and the Savior Jesus Christ that I will keep whatever has been revealed through Christ and His Successors and whatever the first councils and my predecessors have defined and declared.
I will keep without sacrifice to itself the discipline and the rite of the Church. I will put outside the Church whoever dares to go against this oath, may it be somebody else or I.
If I should undertake to act in anything of contrary sense, or should permit that it will be executed, Thou willst not be merciful to me on the dreadful Day of Divine Justice.
Accordingly, without exclusion, We subject to severest excommunication anyone -- be it Ourselves or be it another -- who would dare to undertake anything new in contradiction to this constituted evangelic Tradition and the purity of the orthodox Faith and the Christian religion, or would seek to change anything by his opposing efforts, or would agree with those who undertake such a blasphemous venture."
Note : The above was first written by Pope St. Agatho c. 678 AD but is most likely several centuries older. This oath was taken by all the pontiffs until Pope John-Paul II who did not take it.