Isaiah 38

"Then Hezekiah turned his face toward the wall, and prayed to the Lord, 3 and said, “Remember now, O Lord, I pray, how I have walked before You in truth and with a loyal heart, and have done what is good in Your sight.” And Hezekiah wept bitterly.

4 And the word of the Lord came to Isaiah, saying, 5 “Go and tell Hezekiah, ‘Thus says the Lord, the God of David your father: “I have heard your prayer, I have seen your tears; surely I will add to your days fifteen years... “Behold, I will bring the shadow on the sundial, which has gone down with the sun on the sundial of Ahaz, ten degrees backward.” So the sun returned ten degrees on the dial by which it had gone down."  vv.2-5, 8

Read chapter 38

G'all there's two huge supernatural occurrences right here in these few verses.  One Hezekiah is at the point of death and then bam! gets 15 years added on to his life.  Then the second one is the sun goes back ten degrees.  The first happens because of Hezekiah's sincere repentance that causes God to have mercy on him.  Seems to show God can change His mind due to the free will of people of how they choose to respond.  This also shows that death was worse than life.  If going to heaven is where he would go when he died then why plead for the current life?  Death is a return to the dust (Genesis 3:19) and there's no praise to God in the grave (Ecc.9:10).  Hezekiah would prefer to be able to live for God longer than be in the grave.  Why do you think he'd rather live than die?  

This is the first time in scripture we see record of time-keeping.  The sundial was said to be invented by the Babylonians during Ahaz's time (who was the father of Hezekiah).  "Herodotus (2.109) states that the sundial and the division of the day into twelve hours, were invented by the Babylonians; from them Ahaz borrowed the invention...Josephus thinks these degrees were steps ascending to the palace of Ahaz; the time of day was indicated by the number of steps reached by the shadow. But probably a sundial, strictly so called, is meant;" (BibleHub.com).