Deuteronomy 4:2 in the King James Version
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.
Context
1 Now, Israel, listen to the statutes and to the ordinances which I teach you, to do them, that you may live and go in and possess the land which the LORD, the God of your fathers, gives you.
2 You shall not add to the word which I command you, neither shall you take away from it, that you may keep the commandments of the LORD your God which I command you.
3 Your eyes have seen what the LORD did because of Baal Peor; for the LORD your God has destroyed all the men who followed Baal Peor from among you.