Oneness, Uniqueness of Allah (Tawheed)
Bukhari :: Book 9 :: Volume 93 :: Hadith 607
Narrated Anas:
Allah's Apostle said, "The believers will be assembled on the Day of Resurrection and they will say, 'Let us look for someone to intercede for us with our Lord so that He may relieve us from this place of ours.' So they will go to Adam and say, 'You are Adam, the father of mankind, and Allah created you with His Own Hands and ordered the Angels to prostrate before you, and He taught you the names of all things; so please intercede for us with our Lord so that He may relieve us.' Adam will say, to them, 'I am not fit for that,' and then he will mention to them his mistake which he has committed.' "