Sahih Bukhari Volume 001, Book 002, Hadith Number 021.
Sahih Bukhari Book 02. Belief
Narated By Abu Said Al-Khudri : The Prophet said, "When the
people of Paradise will enter Paradise and the people of Hell
will go to Hell, Allah will order those who have had faith
equal to the weight of a grain of mustard seed to be taken out
from Hell. So they will be taken out but (by then) they will be
blackened (charred). Then they will be put in the river of
Haya' (rain) or Hayat (life) (the Narrator is in doubt as to which
is the right term), and they will revive like a grain that grows
near the bank of a flood channel. Don't you see that it comes
out yellow and twisted."