Psalm 12:6-7 NKJV
The words of the LORD are pure words, Like silver tried in a furnace of earth, Purified seven times.  You shall keep them, O LORD, You shall preserve them from this generation forever.
Psalm 119:72 NASB
The law of Your mouth is better to me Than thousands of gold and silver pieces.
Malachi 3:2-3 NASB
“But who can endure the day of His coming? And who can stand when He appears? For He is like a refiner’s fire and like fullers’ soap.  He will sit as a smelter and purifier of silver, and He will purify the sons of Levi and refine them like gold and silver, so that they may present to the LORD offerings in righteousness.