Proverbs 17:3 in the King James Version
The fining pot is for silver, and the furnace for gold: but the LORD trieth the hearts.
Context
2 A servant who deals wisely will rule over a son who causes shame, and shall have a part in the inheritance among the brothers.
3 The refining pot is for silver, and the furnace for gold, but the LORD tests the hearts.
4 An evildoer heeds wicked lips. A liar gives ear to a mischievous tongue.