Solomon
Proverbs 17:3ESV·traditional attribution

The crucible is for silver, and the furnace is for gold, and the LORD tests hearts.

Matthew Henry Presbyterian @wholebiblehenry

Note, 1. The hearts of the children of men are subject, not only to God's view, but to his judgment: As the fining-pot is for silver, both to prove it and to improve it so the Lord tries the hearts; he searches whether they are standard or no, and those that are he refines and makes purer, Jer 17:10.

John Gill Reformed Baptist @doctorgill

The fining pot is for silver, and the furnace for gold,.... Refiners of silver have their fining pots, in which they purify the silver from the dross; and goldsmiths have their crucibles to melt and purify their gold, by which assays of the worth and value of it may be made; but the Lord trieth the hearts; there is no vessel, as Gersom observes, in...

Jamieson-Fausset-Brown Reformed @jfbcommentary

God only knows, as He tries (Psa 12:6; Psa 66:10) the heart.