In the Bible as the inspired and infallible Word of God and in its sufficiency as our only rule of faith practice.
II Timothy 3:15-16
And how from infancy you have known the holy Scriptures, which are able to make you wise for salvation through faith in Christ Jesus. All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness.
For the word of God is living and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart.