Albert Barnes Commentary 2 Kings 18:16

"At that time did Hezekiah cut off [the gold from] the doors of the temple of Jehovah, and [from] the pillars which Hezekiah king of Judah had overlaid, and gave it to the king of Assyria." — 2 Kings 18:16 (ASV)

Ahaz had already exhausted the treasuries (2 Kings 16:8); Hezekiah was therefore compelled to undo his own work.