Hadith 5574
عَنْ أَبِي هُرَيْرَةَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: أَسْعَدُ النَّاسِ بِشَفَاعَتِي يَوْمَ الْقِيَامَةِ مَنْ قَالَ: لَا إِلَهَ إِلَّا اللَّهُ خَالِصا من قلبه أونفسه رَوَاهُ البُخَارِيّ
Abu Huraira reported the Prophet as saying, "The one who will be most fortunate by reason of my intercession on the day of resurrection will be the one who says there is no god but God sincerely from his heart," or, "his soul." Bukhari transmitted it.