“They devoted themselves to the apostles’ teaching and to fellowship, to the breaking of bread and to prayer.” (Acts 2:42)
Be aware that at this stage of the development of Christianity until a few decades later, there existed nothing like the New Testament as we have it today, and yet the apostles taught the faith to the early Christians.
If the type of some Christians we have today existed in those days, they would have been questioning the apostles, “Where is this in the Bible”, “Where is that in the Bible?”
We should know that it is part of these teachings of the apostles which later became the New Testament. Just the same way not all that Jesus taught and did could have been written in the Bible (John 21:25), the same way not all that the apostles taught (which they received from Jesus) are contained in the Bible.
The Catholic Church calls these teachings and practices which were handed down from the apostles by word of mouth and practice, SACRED TRADITION.
If you do not believe in Sacred Tradition, you have no business believing in the Bible because the Bible is just a part of Sacred Tradition and the latter is older than the former.
And mind you, don’t ask me where this is in the Bible, because I have cited it as Acts 2:42).
2 Thessalonians 2:15 is even more explicit….
Therefore, brethren, stand fast: and hold the traditions, which you have learned, whether by word or by our epistle.
Padre Antonio (Fr. Mawuli Antonio Ahiabor)