The sufficiency of the Holy Scriptures to be the only rule of faith

The Belgic Confession of Faith

Article 7: The Sufficiency of the Holy Scriptures to be the Only Rule of Faith

We believe that those Holy Scriptures fully contain the will of God, and that whatsoever man ought to believe unto salvation is sufficiently taught therein. For since the whole manner of worship which God requires of us is written in them at large, it is unlawful for any one, though an apostle, to teach otherwise than we are now taught in the Holy Scriptures: but even if we, or an angel from heaven, as the Apostle Paul says (Gal. 1:8). For since it is forbidden to add to or take away anything from the Word of God (Deut. 12:32), it does thereby evidently appear that the doctrine thereof is most perfect and complete in all respects.

Neither may we consider any writings of men, however holy these men may have been, of equal value with those divine Scriptures, nor ought we to consider custom, or the great multitude, or antiquity, or succession of times and persons, or councils, decrees or statutes, as of equal value with the truth of God, since the truth is above all; for all men are of themselves liars, and lighter than vapor (Ps. 62:9). Therefore we reject with all our hearts whatever does not agree with this infallible rule, as the apostles have taught us, saying, Test the spirits, whether they are of God (1 Jn. 4:1). Likewise: If anyone comes to you and does not bring this doctrine, do not
receive him into your house (2 Jn. 1:10).