Ecclesiastes 1:13-18
And I gave my heart to seek and search out by wisdom concerning all things that are done under heaven: this sore travail has God given to the sons of man to be exercised therewith.
Nave's Topical Index—AKJV

Ecclesiastes 2:1-12
I said in my heart, Go to now, I will prove you with mirth, therefore enjoy pleasure: and, behold, this also is vanity.
Nave's Topical Index—AKJV

Ecclesiastes 12:9-14
And moreover, because the preacher was wise, he still taught the people knowledge; yes, he gave good heed, and sought out, and set in order many proverbs.
Nave's Topical Index—AKJV