The tradition of the apostles supplanted the tradition of the elders and was both oral and written

On the other hand, our old ways were once new, weren't they?

Why do thy disciples transgress the tradition of the elders? for they wash not their hands when they eat bread.

-- Matthew 15:2

Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.

-- 2 Thessalonians 2:15