Albert Barnes Commentary 2 Chronicles 32:24

"In those days Hezekiah was sick even unto death: and he prayed unto Jehovah; and he spake unto him, and gave him a sign." — 2 Chronicles 32:24 (ASV)

Compare 2 Kings 20:1 and the accompanying notes. The “sign” is not (as the marginal note suggests) the miraculous cure, but the turning back of the shadow on the dial of Ahaz (see 2 Chronicles 32:31).