Salvation from Hellfire

God has said in the Quran:

"Those who have disbelieved and died in disbelief, the earth full of gold would not be accepted from any of them if one offered it as a ransom. They will have a painful punishment, and they will have no helpers."
(Quran, 3:91)

So, this life is our only chance to win Paradise and to escape from Hellfire, because if someone dies in disbelief, he will not have another chance to come back to this world to believe. As God has said in the Quran about what is going to happen for the unbelievers on the Day of Judgment:

"If you could but see when they are set before the Fire (Hell) and say, “Would that we might return (to the world)! Then we would not reject the verses of our Lord, but we would be of the believers!”
(Quran, 6:27)

But no one will have this second opportunity.

The Prophet Muhammad said:
{The happiest man in the world of those doomed to the Fire (Hell) on the Day of Judgment will be dipped in the Fire once. Then he will be asked, “Son of Adam, did you ever see any good? Did you ever experience any blessing?” So he will say, “No, by God, O Lord!”}
Narrated in Saheeh Muslim and Mosnad Ahmad


Source:
A Brief Illustrated Guide To Understanding Islam