NASB 1995
"You may say in your heart, 'How will we know the word which the LORD has not spoken?'

American Standard Version
And if thou say in thy heart, How shall we know the word which Jehovah hath not spoken?

Berean Study Bible
You may ask in your heart, “How can we recognize a message that the LORD has not spoken?”

Douay-Rheims Bible
And if in silent thought thou answer: How shall I know the word that the Lord hath not spoken?

English Revised Version
And if thou say in thine heart, How shall we know the word which the LORD hath not spoken?

King James Bible
And if thou say in thine heart, How shall we know the word which the LORD hath not spoken?

World English Bible
If you say in your heart, "How shall we know the word which Yahweh has not spoken?"

Young's Literal Translation
'And when thou sayest in thy heart, How do we know the word which Jehovah hath not spoken? --

Deuteronomy 18:21 Additional Translations ...