Sahih Bukhari Volume 3, Book 48, Hadith Number 824.

Narated By Abdullah bin Umar : The Prophet said, “Bilal pronounces the Adhan when it is still night (before dawn), so eat and drink till the next Adhan is pronounced (or till you hear Ibn Um Maktum’s Adhan).” Ibn Um Maktum was a blind man who would not pronounce the Adhan till he was told that it was dawn.