2 Thess 2:15 is the most appropriate. Oral tradition was important to preserving teachings in the life of the early Church. Paul is urging his readers to listen to both the written and oral traditions they are being taught.
Acts 2:42 references how the Church devoted themselves to “the apostles’ teachings” (both written and unwritten)
2 Timothy 2:2 is where Paul says to remember “the things you heard me say in the presence of many witnesses”.
1 Cor 11:2 and 1 Thess 2:13 are also worth a glance.
John 21:25 is perhaps my favorite.
You ask where Tradition comes from? Originally, the spoken word and teachings of the apostles, which has been handed on down through the Church Magisterium to the present day.
God bless you.