I said: "O Messenger of Allah ﷺ! Who will be the luckiest person, who will gain your intercession on the Day of Resurrection?" Messenger of Allah ﷺ said: O Abu Huraira! "I have thought that none will ask me about it before you as I know your longing for the (learning of) Hadiths. The luckiest person who will have my intercession on the Day of Resurrection will be the one who said sincerely from the bottom of his heart "None has the right to be worshipped but Allah." (Using translation from Bukhārī 99)  

قُلْتُ يَا رَسُولَ اللهِ مَنْ أَسْعَدُ النَّاسِ بِشَفَاعَتِكَ يَوْمَ الْقِيَامَةِ؟ فَقَالَ النَّبِيُّ ﷺ لَقَدْ ظَنَنْتُ يَا أَبَا هُرَيْرَةَ أَنْ لَا يَسْأَلَنِي عَنْ هَذَا الْحَدِيثِ أَحَدٌ أَوَّلَ مِنْكَ لِمَا رَأَيْتُ مِنْ حِرْصِكَ عَلَى الْحَدِيثِ أَسْعَدُ النَّاسِ بِشَفَاعَتِي يَوْمَ الْقِيَامَةِ مَنْ قَالَ لَا إِلَهَ إِلَّا اللهُ خَالِصًا مِنْ قِبَلِ نَفْسِهِ