1 Corinthians 3:20
"And again, The Lord knoweth the thoughts of the wise, that they are vain."
Cross References (ranked by relevance)
Psalm 94:11
27
The LORD knoweth the thoughts of man, that they are vanity.
Colossians 2:8
Beware lest any man spoil you through philosophy and vain deceit, after the tradition of men, after the rudiments of the world, and not after Christ.
Romans 1:21
Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
Psalm 2:1
Why do the heathen rage, and the people imagine a vain thing?