Sahih al-Bukhari, Volume 8, Book 76, Hadith 431 (USC-MSA) ⓘ

Narrated `Utban bin Malik Al-Ansari: who was one of the men of the tribe of Bani Salim: Allah's Messenger 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 ‏" ‏‏.‏