On the other hand, Tradition is Scriptural: it is, for example, mentioned by Paul, particularly to the church of the Thessalonians:
"Therefore, brethren, stand fast and hold the traditions you were taught whether by word or our epistle." (2 Thess 2:15)
Notice that Paul doesn't elevate one mode of receiving the Tradition--his oral word or his written epistle--above the other; the authority is the same. Though we can't be sure that the content is exactly the same in every single detail of the oral and written forms, we can surmise that they testify to the same material Truth and therefore don't contradict one another. From another one of Paul's letters, this time to Timothy, it seems that this oral Tradition at the very least refers to (and consists of) the specific body of teaching and doctrine that was handed down by the Apostles:
"Hold fast the sound pattern of words which you have heard from me." (2 Tim 1:13)
So, there was a "sound pattern" of oral teaching recognizable to Timothy (and presumably to the others taught by the Apostles) which was to be kept and by which the early Christians could recognize truth from error. By this "sound pattern" the early Christians could therefore "rightly divide" the word of truth. On the other hand those who did not hold fast the "sound pattern of words" received orally from the Apostles could be considered "untaught and unstable" (2 Peter 3:16) and were liable to misinterpret the Apostle's writings (and the other Scriptures) and thus to "twist the Scriptures to their own destruction".
What's more is that Paul expects Timothy to be able to transmit orally that which he received from Paul: "And the things you have heard from me among many witnesses, commit these to faithful men who will be able to teach others also." (2 Tim 2:2). Notice here that the "things" Timothy received were not exclusive or private but were heard "among many witnesses", and how the faithful men to whom Timothy committed these "things" were to teach others as well (that's four generations of oral transmission). The public reception of the Tradition in the community could thus serve as a "check" or "balance" on those who would deviate from the "sound pattern" while claiming (ie like the Gnostics did) to be handing down some new teaching allegedly received "secretly" from the Apostles.
If one can be in any doubt as to the Scriptural basis of this idea of Tradition, and its corollary, Apostolic Succession, then there are ample examples to support it:
Paul ordains presbyters in Lystra, Iconium and Pisidian Antioch in Acts 14:23 and bishops at Ephesus in Acts 20:28 to carry on his work in those places; later, Timothy is bishop at Ephesus (1 Tim 1:3) having been ordained (1 Tim 4:14; 2 Tim 1:6) and Paul gives him instructions on how to select bishops and deacons (1 Tim 3) and also to keep the Tradition of teaching given to him orally by Paul (2 Tim 1:13-14; 3:14) as well as Scripture (2 Tim 3:15-17); similarly, Paul writes to Titus, to whom he has delegated his authority to appoint presbyters in Crete (Titus 1:5-6) and here he gives similar 'selection instruction' as to Timothy, also referring (Titus 1:7-9) to qualifications for a bishop, including "holding fast to the Word of God as he was taught it" in order to pass on sound doctrine to others (Tradition). It is likely that in the Pastoral letters the references to qualifications for 'bishops' are first and foremost to Timothy and Titus personally, in their capacities as bishops of Ephesus and Crete respectively. In any event, here we have the following elements in these passages:-
1. Paul, an Apostle, appoints bishops and presbyters to continue his work in the various congregations he has founded or helped set up.
2. These officers have been grounded in the Scriptures but also taught orally by Paul. They are thus steeped in both Scripture and Tradition.
3. They are charged with teaching others the above and also with pastoral care of the flock
4. They are also charged with ordaining others to similarly carry on that work and are given criteria for selection of those successors.
Therefore, we have Scripture and Tradition plus Apostolic Succession in a nascent form within the pages of the NT.