"Where in the Bible does it say that the Bible is our only source of God's Truth? Answer: nowhere"
Uh, how about reading this...
2Ti 3:15 And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus.
2Ti 3:16 All scripture [is] given by inspiration of God, and [is] profitable for doctrine, for reproof, for correction, for instruction in righteousness:
2Ti 3:17 That the man of God may be perfect, throughly furnished unto all good works.
And then read....
Gal 1:6 I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel:
Gal 1:7 Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.
Gal 1:8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
Same with the Old Testament - Jews were first and then the books were written. Moses was before books of Moses and Prophets were before the books of Prophets, David was before the Psalms and Kings were before the books of Kings.