Paul's knowledge of Jannes and Jambres the magicians of Egypt Per Paul in:

2 Timothy 3:8 ESV


  Just as Jannes and Jambres opposed Moses, so these men also oppose the
  truth, men corrupted in mind and disqualified regarding the faith.


Which is cross referenced to:

Exodus 7:11 ESV


  Then Pharaoh summoned the wise men and the sorcerers, and they, the
  magicians of Egypt, also did the same by their secret arts.


and also

Acts 13:8 ESV


  But Elymas the magician (for that is the meaning of his name) opposed
  them, seeking to turn the proconsul away from the faith.


Titus 1:16


  They profess to know God, but they deny him by their works. They are
  detestable, disobedient, unfit for any good work.


How did Paul know the names of the Magicians since they appear to not be mentioned anywhere else in the bible by name?  And how was this cross reference made (how do we really know that he's talking about the same story)?

The only link that I can find is from the Damascus Document which I was led to from reading Moses in Biblical and Extra-Biblical Traditions by Axel Graupner, Michael Wolter.

I'm going to ask this over at Hermeneutics too.  However I feel that this is an interesting doctoral question too.
It's  in the Babylonian Talmud.

Torah comprises the Pentateuch in the main, but also the rest of the OT, as well as the commentaries, ie Talmud.

See also:

Who were Jannes and Jambres?