Sahih Bukhari Volume 008, Book 076, Hadith Number 506.

Narated By Jundub : The Prophet said, "He who lets the people hear of his good deeds intentionally, to win their praise, Allah will let the people know his real intention (on the Day of Resurrection), and he who does good things in public to show off and win the praise of the people, Allah will disclose his real intention (and humiliate him).