The Legend of Evil King Hirankashyap
Thus the demon king ordered Prahlad to sit on a pyre (a structure, usually made of wood, for burning a body as part of a funeral rite or execution) along with Holika (who was immune to fire) the sister of the demon king.
When the fire started, Holika was burnt to death in spite of her immunity to fire, and miraculously Prahlad was saved because Prahlad sought the help of Lord Vishnu during the event