three young friends of the prophet daniel. The story of how they were saved from the furnace of king nebukadnessar is told in chapter three of the book of daniel in the holy bible (as quoted from the new international version):

1 King Nebuchadnezzar made an image of gold, ninety feet high and nine feet wide, and set it up on the plain of Dura in the province of Babylon.2 He then summoned the satraps, prefects, governors, advisers, treasurers, judges, magistrates and all the other provincial officials to come to the dedication of the image he had set up. (...)4 Then the herald loudly proclaimed, "This is what you are commanded to do, O peoples, nations and men of every language:5 As soon as you hear the sound of the horn, flute, zither, lyre, harp, pipes and all kinds of music, you must fall down and worship the image of gold that King Nebuchadnezzar has set up.6 Whoever does not fall down and worship willimmediately be thrown into a blazing furnace."after this, some astrologers accuse daniels friends (Shadrach, Meshach and Abednego) of not worshipping the statue. they are brought before the king.14 and Nebuchadnezzar said to them, "Is it true, Shadrach, Meshach and Abednego, that you do not serve my gods or worship the image of gold I have set up?(...)16 Shadrach, Meshach and Abednego replied to the king, "O Nebuchadnezzar, we do not need to defend ourselves before you in this matter.17 If we are thrown into the blazing furnace, the God we serve is able to save us from it, and he will rescue us from your hand, O king.18 But even if he does not, we want you to know, O king, that we will not serve your gods or worship the image of gold you have set up.

Nebuchadnezzar is furious and commands that they must be thrown in the furnace.

23 and these three men, firmly tied, fell into the blazing furnace.24 Then King Nebuchadnezzar leaped to his feet in amazement and asked his advisers, "Weren't there three men that we tied up and threw into the fire?"
They replied, "Certainly, O king."25 He said, "Look! I see four men walking around in the fire, unbound and unharmed, and the fourth looks like a son of the gods." (this fourth figure is seen by some interpreters as an early appearance of jesus).26 Nebuchadnezzar then approached the opening of the blazing furnace and shouted, "Shadrach, Meshach and Abednego, servants of the Most High God, come out! Come here!" So Shadrach, Meshach and Abednego came out of the fire,27 and the satraps, prefects, governors and royal advisers crowded around them. They saw that the fire had not harmed their bodies, nor was a hair of their heads singed; their robes were not scorched, and there was no smell of fire on them.28 Then Nebuchadnezzar said, "Praise be to the God of Shadrach, Meshach and Abednego, who has sent his angel and rescued his servants! They trusted in him and defied the king's command and were willing to give up their lives rather than serve or worship any god except their own God.29 Therefore I decree that the people of any nation or language who say anything against the God of Shadrach, Meshach and Abednego be cut into pieces and their houses be turned into piles of rubble, for no other god can save in this way."30 Then the king promoted Shadrach, Meshach and Abednego in the province of Babylon.