Catholics get asked this question by sola scriptura Protestants now and then about our teachings and practices.

Now you can ask them the same thing. Tomorrow’s Gospel reading closes with an allusion to a prophecy: “He went and dwelt in a town called Nazareth, so that what had been spoken through the prophets might be fulfilled, He shall be called a Nazorean.”

We’re used to the Gospel readings this time of year being full of Old Testament prophecies coming from Isaiah and Daniel, but this one, about Christ being “called a Nazorean,” is nowhere to be found in Scripture. It’s most likely an example of Jewish Sacred Tradition.

The Catholic Answers forum pages discussed this topic a few years ago.