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كتاب الإيمان
2  
Belief
(33)
Chapter: Faith increases and decreases
(33)
باب زِيَادَةِ الإِيمَانِ وَنُقْصَانِهِ
Sahih al-Bukhari 44

Narrated Anas:

The Prophet (ﷺ) said, "Whoever said "None has the right to be worshipped but Allah and has in his heart good (faith) equal to the weight of a barley grain will be taken out of Hell. And whoever said: "None has the right to be worshipped but Allah and has in his heart good (faith) equal to the weight of a wheat grain will be taken out of Hell. And whoever said, "None has the right to be worshipped but Allah and has in his heart good (faith) equal to the weight of an atom will be taken out of Hell."

حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا هِشَامٌ، قَالَ حَدَّثَنَا قَتَادَةُ، عَنْ أَنَسٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ يَخْرُجُ مِنَ النَّارِ مَنْ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ، وَفِي قَلْبِهِ وَزْنُ شَعِيرَةٍ مِنْ خَيْرٍ، وَيَخْرُجُ مِنَ النَّارِ مَنْ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ، وَفِي قَلْبِهِ وَزْنُ بُرَّةٍ مِنْ خَيْرٍ، وَيَخْرُجُ مِنَ النَّارِ مَنْ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ، وَفِي قَلْبِهِ وَزْنُ ذَرَّةٍ مِنْ خَيْرٍ ‏"‏‏.‏ قَالَ أَبُو عَبْدِ اللَّهِ قَالَ أَبَانُ حَدَّثَنَا قَتَادَةُ حَدَّثَنَا أَنَسٌ عَنِ النَّبِيِّ صلى الله عليه وسلم ‏"‏ مِنْ إِيمَانٍ ‏"‏‏.‏ مَكَانَ ‏"‏ مِنْ خَيْرٍ ‏"‏‏.‏
Reference : Sahih al-Bukhari 44
In-book reference : Book 2, Hadith 37
USC-MSA web (English) reference : Vol. 1, Book 2, Hadith 43
  (deprecated numbering scheme)