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كتاب الرقاق
81
To make the Heart Tender (Ar-Riqaq)
(6)
Chapter: The deed which is done seeking Allah's Countenance
(6)
باب الْعَمَلِ الَّذِي يُبْتَغَى بِهِ وَجْهُ اللَّهِ
Sahih al-Bukhari 6423

Narrated `Utban bin Malik Al-Ansari:

who was one of the men of the tribe of Bani Salim: Allah's Messenger (ﷺ) came to me and said, "If anybody comes on the Day of Resurrection who has said: La ilaha illal-lah, sincerely, with the intention to win Allah's Pleasure, Allah will make the Hell-Fire forbidden for him."

قَالَ سَمِعْتُ عِتْبَانَ بْنَ مَالِكٍ الأَنْصَارِيَّ، ثُمَّ أَحَدَ بَنِي سَالِمٍ قَالَ غَدَا عَلَىَّ رَسُولُ اللَّهِ صلى الله عليه وسلم فَقَالَ ‏ "‏ لَنْ يُوَافِيَ عَبْدٌ يَوْمَ الْقِيَامَةِ يَقُولُ لاَ إِلَهَ إِلاَّ اللَّهُ‏.‏ يَبْتَغِي بِهِ وَجْهَ اللَّهِ، إِلاَّ حَرَّمَ اللَّهُ عَلَيْهِ النَّارَ ‏"‏‏.‏
Reference : Sahih al-Bukhari 6423
In-book reference : Book 81, Hadith 12
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 431
  (deprecated numbering scheme)