Deuteronomy 4:1,2 (KJV)
1 Now therefore hearken, O Israel, unto the statutes and unto the judgments, which I teach you, for to do them, that ye may live, and go in and possess the land which the Lord God of your fathers giveth you.
2 Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the Lord your God which I command you.
Deuteronomy 12:28:32 (KJV)
28 Observe and hear all these words which I command thee, that it may go well with thee, and with thy children after thee for ever, when thou doest that which is good and right in the sight of the Lord thy God.
29 When the Lord thy God shall cut off the nations from before thee, whither thou goest to possess them, and thou succeedest them, and dwellest in their land;
30 Take heed to thyself that thou be not snared by following them, after that they be destroyed from before thee; and that thou enquire not after their gods, saying, How did these nations serve their gods? even so will I do likewise.
31 Thou shalt not do so unto the Lord thy God: for every abomination to the Lord, which he hateth, have they done unto their gods; for even their sons and their daughters they have burnt in the fire to their gods.
32 What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it.
Proverbs 30:5-6 (KJV)
5 Every word of God is pure: he is a shield unto them that put their trust in him.
6 Add thou not unto his words, lest he reprove thee, and thou be found a liar.
Revelation 22:18,19 (KJV)
18 For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book:
19 And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.