From Sahih Bukhari (Hadith 99):
Narrated Abu Huraira:I said: "O Allah's Messenger (ﷺ)! Who will be the luckiest person, who will gain your intercession on the Day of Resurrection?" Allah's Messenger (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
Reference: Bukhari 99