Catholics believe that Scripture and Tradition are inseparably linked and that they, together, form the two witnesses to the one revelation of God, Jesus Christ.
What is tradition and where did it come from? Catholics believe that tradition is the deposit of faith which was given to the early Church by Christ through his Apostles which pre-dates the New Testament and has been passed on to us today. Over time the tradition has evolved as our understanding of Jesus and all he accomplished has deepened but the original deposit of faith remains unchanged. Just one of the evident effects of the deepening of this understanding is the Church's decision to compile together what earlier was viewed as a haphazard collection of letters and texts and come to venerate them as Sacred Scripture.
Tradition passes the faith on through the liturgies of the Church, its Sacraments, artwork, music, hymnology, sermons, the writings of the saints and the yearly calendar with its feasts and fasts. For the first 1500 years of Christianity, before the invention of the printing press, this was the only way in which the Gospel could be passed on and it is a tool given to us by Christ to do just that.
Can you find Tradition in Scripture? Of course! The New Testament is riddled with allusions to things taught by Christ that are not recorded in the text.
Other references include: Mk 4:33, Mk 6:34, Jn 16:12, Jn 21:25, Acts 1:2-3.
Now we also find in the scriptures two words related to παράδοσις; namely παραδίδωμι and παραλαμβάνω. These speak of tradition delivered and tradition received as the faith is passed on, not forgetting that this is what tradition is; the passing on of faith.