Tradition, right? Not Scriptural.
Yes, apostolic tradition.
As Jesus ascended into heaven, He didn't yell down: READ MY BOOK! There WAS no book. The apostles didn't write things down until later. Paul didn't write until after Jesus death either. Yet Jesus' Church grew, WITHOUT the written words, WITH the preaching of the Apostles and the 72 other disciples Jesus appointed. They didn't carry books and scrolls around with them. They preached according to the tradition taught to them by Jesus.
There were scrolls of the life of Jesus scattered throughout early Christiandom, but darn few and even fewer people read. Apostolic tradition was the way the Church grew for a LONG time. Remember that John said: "There are, however, many other things that Jesus did: but if every one of these should be written, not even the world itself, I think, could hold the books that would have to be written." (John, 21:25)
Jesus did much more during His life but they weren't written down. He left it to his Apostles to spead the Good News...thereby NOT relying on just a book.