All Christians believe in infallible teaching and an infallible teaching authority. After all, what good is it to hear the gospel message of salvation if it's untrue? Christians have various views of where we find infallible teaching. All true Christians agree that the Bible is the inspired, inerrant, infallible word of God.
Every infallibly true Christian teaching came from one of two sources:
True Christianity, of course, rejects option #2. Apostolic revelation ended with the apostles. All infallible teaching we today possess was taught to the apostles by Jesus Christ and the Holy Spirit and the apostles passed it on to subsequent generations.
All infallible truth was passed-down from the apostles. There is no other source of infallible truth other than apostolic teaching.
The celibate priesthood is an example of a teaching the Catholic Church claims to have always taught but obviously hasn't — because the apostles didn't teach it.