Isaiah 38:7 gives the actual sign (the shadow) that fulfills Hezekiah's request for a sign he will go to the temple.

Isaiah 7:11 commands Ahaz to ask a sign from God; Hezekiah does ask, showing a similar appeal but different response.

2 Kings 20:8 is the parallel verse where Hezekiah asks Isaiah for a sign to confirm his healing.

2 Kings 20:5 records the same promise: Hezekiah will go up to the house of the Lord on the third day, directly answering his question.

2 Chronicles 32:24 confirms God gave Hezekiah a sign, directly parallel to the sign request here.