Well, technically that was a paraphrase, but it was based on Revelation 22:18-19:
18For 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:
19And 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.
Also:
Deuteronomy 4:2
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.
Proverbs 30:5-6
Every word of God is pure: He is a shield unto them that put their trust in Him. Add thou not unto His words, lest He reprove thee, and thou be found a liar.
I have to be honest and say I didn't know exactly where the verses were found in the Bible, but I knew there was at least one within the confines of Revelation.
Anyway, I hope that helps.