Sahih Bukhari Volume 1, Book 2, Hadith 22

حَدَّثَنَا إِسْمَاعِيلُ، قَالَ حَدَّثَنِي مَالِكٌ، عَنْ عَمْرِو بْنِ يَحْيَى الْمَازِنِيِّ، عَنْ أَبِيهِ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ يَدْخُلُ أَهْلُ الْجَنَّةِ الْجَنَّةَ، وَأَهْلُ النَّارِ النَّارَ، ثُمَّ يَقُولُ اللَّهُ تَعَالَى أَخْرِجُوا مَنْ كَانَ فِي قَلْبِهِ مِثْقَالُ حَبَّةٍ مِنْ خَرْدَلٍ مِنْ إِيمَانٍ‏.‏ فَيُخْرَجُونَ مِنْهَا قَدِ اسْوَدُّوا فَيُلْقَوْنَ فِي نَهَرِ الْحَيَا ـ أَوِ الْحَيَاةِ، شَكَّ مَالِكٌ ـ فَيَنْبُتُونَ كَمَا تَنْبُتُ الْحِبَّةُ فِي جَانِبِ السَّيْلِ، أَلَمْ تَرَ أَنَّهَا تَخْرُجُ صَفْرَاءَ مُلْتَوِيَةً ‏"‏‏.‏ قَالَ وُهَيْبٌ حَدَّثَنَا عَمْرٌو ‏"‏ الْحَيَاةِ ‏"‏‏.‏ وَقَالَ ‏"‏ خَرْدَلٍ مِنْ خَيْرٍ ‏"

Narrated 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."