“In those days King Hezekiah became sick. He was at the point of death. He prayed to Yahweh. Yahweh answered him and gave him a sign. But King Hezekiah did not respond according to the benefit done to him. His heart was proud. Therefore wrath came upon him, Judah, and Jerusalem. However, King Hezekiah humbled himself for the pride of his heart, both he and the inhabitants of Jerusalem. Thus the wrath of Yahweh did not come upon them in the days of King Hezekiah.”
This is a summary of the longer story 2 Kings, chapter 20. King Hezekiah became so sick that he was dying. The prophet Isaiah came to him and said that he should get his house in order. He was going to die and not recover. Since the prophet had spoken, what else was there to do? King Hezekiah prayed and wept to Yahweh. He said that he had tried to walk correctly in the sight of Yahweh with his whole heart. Then Yahweh came to Isaiah to tell King Hezekiah that he has heard his prayer. He had seen his tears so that he would heal him. Yahweh was going to add 15 years to his life. Isaiah then healed King Hezekiah. However, King Hezekiah wanted a sign that Yahweh had healed him. Isaiah cried to Yahweh and the sundial moved back 10 intervals to show the curing of King Hezekiah. This indicated that the sun had moved backwards which would have been miraculous. All this is left out of this summary statement here.